JG,
It depends on the scope. I once used a 5-15x variable, made by a major European company, on a prairie dog shoot. The scope and rifle weren't mine, but were provided by a rifle company. The scope had no provision for parallax correction, and out at 400 yards it was almost impossible to hit a prairie dog, because the scope had at least a foot of parallax. (The company doesn't make that scope anymore.)
Now, I could have eliminated the parallax by keeping my eye far enough behind the scope to eliminate most of the field of view, by keeping the exit pupil centered in the visible field around the crosshairs. But that seems kind of silly, when it's easy enough to provide some sort of parallax correction on higher-powered scopes.
Have also encountered considerable parallax at 300-400 yards with 3-9x scopes turned all the way up, and even a few fixed powers. You never know until you test 'em.
