bleeb
Contributor
As others have mentioned, a good fit to minimize water flow in and out is important. However, it shouldn't be so tight as to constrict blood flow, or stretch and decrease insulation. (That's the compromise with the stretchy neoprenes vs the regular ones.)
A lesser issue is that neoprene's insulating value slowly breaks down as it's compressed and re-expands. Roughly speaking, considerable insulating value may have been lost after a couple of hundred deep dives. Rental suits often get a lot of use this way, and might not be as effective if not new. Folds and creases are also immediately bad, although the small area reduces the impact.
A lesser issue is that neoprene's insulating value slowly breaks down as it's compressed and re-expands. Roughly speaking, considerable insulating value may have been lost after a couple of hundred deep dives. Rental suits often get a lot of use this way, and might not be as effective if not new. Folds and creases are also immediately bad, although the small area reduces the impact.