your blind spot (behind you) is not the deer's blind spot....it stinks hearing a noise behind you that sounds like a deer and you know they might be looking at you....so you have to sit there motionless while the deer does its thing
with a stand, if you hear something behind you, then you at least know the deer probably can't see you either....if you have your bow in your lap or on your seat with a third hand holder...then you can slowly get it ready to go, especially if you know you are up pretty high and there is cover behind you (edit: and you aren't in a super skinny tree)
this is a really big deal to me and i'm surprised it isn't brought up more
this and the easier ability to take shots to your right (for a rightie) are the only advantages i see with a traditional hang on stand