I have a bow rest mounted on the platform of my climbing stand, yet I still hold my bow more often than not. If I'm holding it, I'm better prepared to take a shot with less movement than if I have to reach, grab the bow, lift it into position, take aim, and shoot. That's more movement than I have time for if a deer comes in from an unexpected direction. Sure, it's more comfortable to use the rest, but if I want total comfort I may as well stay in my living room.
I typically just use the rest for the first hour I'm in my stand (e.g. when it's dark) and when I'm letting the woods settle down after taking the stand. After that, I hold it.