I'm a very seasoned 3D veteran and I still range my animal every time right before the shot be it 20 yards or 42 yards.

I wear my rangefinder on my chest with a Crooked Horn Outfitter bino strap. I know what 20 yards looks like, I know what 30 yards looks like but I don't want leave anything to chance. It's just a habit, rangefinder in one hand, bow in the other, range, release on, draw, anchor, aim, release..it's mechanical.