Adjustable or fixed paralax?

When shooting F-class or similar practical/tactical competitions with shots ranging from 100 - 700 yards (or more), is a shooter at a disadvantage if they choose a scope with fixed paralax? If so, how much of a disadvantage?

With a fixed paralax scope, say set at 100 yards, at what distance does the scope become a hindrance and affect the shot to a significant amount, and what is a significant amount defined as?

And along similar lines - does anyone use an adjustable paralax scope for hunting (deer/hog) and target shooting?

I understand adjustable paralax and the benefits. I have one scope that has an adjustable objective mounted on a .223 bolt gun. I can't imagine sitting in a tree stand or ground blind, looking over a field with shots available up to 400 yards, and having to quickly range the target and then adjust paralax.

I'd like to find a scope that could be used for competition as well as hunting.