Depends on the stand you are using. Some with the setup they have are not friendly to shoot from a seated position. Bars getting in the way also you may find taking a shot going around your tree to be impossible.

You have just as much of a chance spooking the deer picking up the bow and drawing seated as you would slowly standing and drawing. It all comes down to being quiet and trying to go as unnoticed as possible.

Also to note most hunters practice shooting from the ground standing. Adding a tree stand to the mix you should also practice shooting from heights to learn the angles and how your shots are just to get the experience. Adding a seated position would say practice that as well. Me and my old neighbor got 2 trees in our back yard we use to shoot from just to practice.