As per a suggestion from one of my players I'm going to make a post about zone versus man and when I think each should be played. Now, this is a very difficult question to answer because I think the answer is different depending on the level of ultimate. I would probably say completely different things for league play, versus club, versus college, and I'm not even going to speculate on women's (no experience there), but given that it's just about college regionals, I'm going to focus this blog on my opinion for college teams.
For starters, anyone who's played on teams that I've coached or captained knows that I am a big fan of zone in college. In general college throwers are less experienced, don't necessarily have a complete range of throws (all the breaks, over-the-tops, etc), and have a greater tendency to make poor decisions given that lack of experience.
However, I have a very different perspective as to when to play zone versus man, given the conditions. So I'm going to through several different conditions that people tend to see and why I'd play zone or man in that situations. Before I do that however I'm gonna go over some basic zone stuff.
A zone can do a handful of different things. First and foremost it disrupts the opposing team's offense. Playing zone forces a team out of their base offense into something that usually resembles a horizontal stack, with horizontal poppers and deeps spread out with 3-4 handlers behind the disc.
Secondly, a zone should be forcing the offense to make a greater number of throws. In general, there won't be a deep option because of the nature of zone, so the offense is forced to make many more throws than one-two huck.
Thirdly, a zone can be a simple disruption play. If the opposing team has a successful pull-play they like to run or whatnot, like a center stack or Boston, zone can force them out of that pull offense, then settle back into man after a handful of throws, similar to the disruption I talked about in my first point.
Lastly, a zone can be an equalizing factor. If your team struggles matching up physically with another team, then a zone can be something that puts things on more even ground as it allows your best deep always to be last back and limits the advantages the opposing team if they are more athletic.
I absolutely detest teams that play zone going upwind. I realize that throws are difficult, deep throws and over the tops are limited, but what it boils down to, is those things are all true for man as well. When you're playing a zone, you're allowing their best throwers to consistently get the disc and be able consistently make their throw of choice (for me personally, I love always having a backhand option as an offensive handler, and against a zone defense I probably throw close to 85% backhands). If you're read my thread on flat marking, then you know that I think a solid flat mark with good fronting underneath is the defense of choice for upwind situations. If you're doing this well then you're taking away both the inside-out forehand and backhand and are not allowing the thrower to step forward into their throw, making every throw except something that goes straight behind very challenging.
When there is a significant downwind I think that zone is the oftentimes the best option. In college, most (not all, but most) teams are looking for a quick deep strike on downfield points, so as to win the field position game and not give the defense a break opportunity in the offense's upwind half of the field. Playing a zone gives you several advantages if the game has turned into more of a punt/field position scenario. First of all, you're putting your best deep defender (at least I hope you are), back to stop the look that they are mostly actively going for. Secondly, depending on the zone you're playing (I like a 3 or 4 man force middle contain in this situation), you're forcing them to make at least a handful of swings before they put a deep or over the top throw out there. The swings themselves are either going straight behind, which is an upwind throw, or they're moving across the field horizontally, making them a bit more difficult crosswind throw.
Additionally, if you do force a turn on those swings, you have a numbers advantage, as your entire cup is theoretically somewhere near the disc. So the fast break opportunity is easy, and as my teams have heard me say a million times, wind games are won in transition.
Some people argue that over the tops are too easy going downwind, and the offense can simply throw over your cup. This is true, but whatever that throw is, it is, at the very least, a slightly lower percentage throw than a classic backhand or forehand, and assuming you play a decent zone, you're going to be forcing an over-the-top throw somewhat far downfield where you deep has a good chance to get a D.
This is a tough answer. Running a trap to the wind side of the field can often result in a turnover if you're able to get the disc fully trapped. Also flat-marking isn't as effective as the crosswind allows for looser inside out breaks and hucks.
I more often than not end up playing man in this situation, because a smart team is not easily trapped, and even from that trap-side of the field the deep punt from there is not super difficult. So in general I'd say play man in this situation, forcing with the wind, meaning the open-side throw is the direction the wind is blowing. This does two things. First, it makes an around break a fairly upwind throw, allowing your marks a bit more leniency in shifting flatter to take away the inside-out break. Because the break threat is less, your downfield defenders are given more leeway to play harder on the open side, forcing the disc inevitably to the side of the field where the wind can keep a thrower/offense somewhat trapped on it's own.
Zone, zone zone! The disc is wet, catching is harder, throwing is harder. The more throws you can force an offense to make, the more chances you have for forcing a turnover. Obviously, that logic is true in any conditions, but given an average college players' general ability to catch and throw, the percentage increase from the wet disc and cold conditions make this an ideal time to play zone and force the opposing team to throw more throws than they'd prefer. Additionally, upside-down throws are significantly more difficult to catch when the disc is wet, making a zone that forces the offense to make over-the-top throws (like a 4 man cup) ideal. At the very least start in zone to disrupt the huck play, then as the field length shortens transition to man.
But what about that annoying metro east team that always plays zone in any conditions and we can't figure it out and we're sad and we just lost to a bunch of short fat guys:
I've played against several teams that play zone close to 100% of the time (mostly east coast teams for some reason), and while I'm not going to say it's awful, I will say that in general I think that is very poor strategy. If you're teaching your team to play zone even a majority of the time then you're using up time that can be spent learning good solid man (especially for young players).
Even if you spend all year on your zone and it's very successful and you run it to perfection, ONE THROWER can beat it. And if that's the case, that one elite thrower, just took out your whole team strategy.
Three years ago at regionals we played CU in pool play. There were minimal conditions, but our defensive game plan was to play our 4 man cup-contain (which we had practiced diligently all year), to limit their hucking game and force them to beat us with over the top throws, since they were the more athletic team. We executed the zone very well, they were able to swing, but not able to gain yards, and we were able to limit their deeps and keep them in the middle of the field. After about 5 throws they put the disc in Mac Taylor's hands and he threw a 50 yard line-drive hammer down field to the space we were leaving open, zone broken. He threw exactly what we were trying to force, a challenging over the top throw, that was the whole point of our zone. The next point he did it again, and the point after. At that point I looked at my defensive captain and we both agreed, ok, they can consistently make that throw, gotta try something else. My overall point here was this, they had one extraordinary thrower, and he alone broke our entire defense. If you're team is a team based entirely on zone, you may beat some teams, sure, but every pretty good college team has at least that one big thrower, that can put the disc anywhere on the field, so if there aren't enough conditions backing your scheme, you're screwed.
In the end, a lot of zone/man options are based on what the other team is doing or their strengths and weaknesses, but in general as you get to higher and higher levels of the sport from elite college up to elite club and whatnot, you see less and less zone because the better the throwers the less functional any zone gets.