I think yes to all of those things.
My understanding is a lot of colleges these days are using sophisticated yield models to track how they are doing in terms of various institutional goals. They may also have some fairly specific boxes to check (the famous orchestra tuba player from North Dakota), and so on. But there is always uncertainty about the best ways to optimize across all these goals.
And so they have various ways of managing uncertainty. The waitlist is the obvious one, and I understand very often they will try to check unchecked boxes off the waitlist. But more broadly, they do things like come up with provisional decisions, and then adjust some actual decisions at the end to optimize the admit class in light of their yield model.
Deferral is really just another mechanism like that, delaying a truly final decision until they can optimize their admit class.
But they canāt defer everyone, indeed ED schools presumably get the best results when locking in some people they know they really want, and then building the rest of the admit class around them.
OK, so at a high level, ED admit versus deferral is a decision between whether you want to lock in and build around that applicant, or wait to see whether admitting them really optimizes your yield model. And for that matter, deferral versus denial is about whether you want to wait or if you basically know there is no real chance they will end up being admitted in the final optimization.
That last is a bit fuzzy and you can see why some colleges used to hand out a lot of deferrals. I mean, what is really in it for them to cancel an option, even if there is only a tiny chance they will want to exercise that option? But people pointed out how unfair that was, and pressured these colleges to deny more kids.
All right, so if you are deferred, it means two things basically. You were not so compelling they knew they wanted to build the admit class around you. But, at least if they are being ethical about it, you might still be part of the final admit class depending on how it evolves. And again, assuming ethical deferrals, they legitimately donāt know yet how that will break.