It is a good idea to practice, at least occassionally, from different positions.

Last year I learned how important it is....twice!!!

I blew a chance at a doe that came over a rise quickly on a trail that would have taken her right by me.
I was on the ground following the trail and she surprised me. She was so close, I had to freeze the instant I saw her. She saw me as I raised my bow to ready myself in case she gave me a broadside shot. She moved off to my right, and I couldn't even draw since I had stopped in mid-stride with my right leg forward.

Then, with the buck I did get from a treestand, I hit him high and too far back because he was off to my right as well. When he came out of the bushes, he was only 15 yards from me. Again I had to freeze. I was able to draw unseen, but executed a less-than-perfect shot and torqued it bad. If it hadn't hit him in the spine, which allowed me a follow up DL, he'd be hurt or dying slowly, and I'd be feeling like hanging up my bow.

Now, I make sur eto be ready by practicing from different positions, and putting more thought into how I place my feet in case I get caught with a deer appearing out of nowhere. (They do that, you know)