Yepper, it's important in any scenario where you are shooting on severe up and downhill angles. Out of a treestand is critical, because nearly every shot will be on a hard angle.

Here's a picture of me from this past weekend @ full draw on a 43 yard bedded buck on a sharp angle downhill.........an improperly adjusted 3rd axis could easily throw this arrow way out of the 10 ring, and that's not nearly as hard of an angle as a treestand could produce. I use a Medicine Stone jig for setting my third axis along with a HTM string attachable level.