I disagree with the semantics here. Permanent is not a word that applies to most modifications. Usually, if it can be done, it can be undone.
Drilling holes in a fender for a snorkel makes the fender unusable otherwise, but a new fender is like $40 plus paint.
Nor does drilling a few holes for fasteners doesn't make a frame/underbody mod permanent.
i'm two years in and many adventures through the sw U.S. with our 4runner TE, and thus far without sliders...however, i'm currently seriously considering something high and tight...we've had some difficult lines occasionally to avoid chancing contact at the rocker panels...nothing that has really limited us though, so i don't consider them necessary--but perhaps appreciated for the opportunities we might have with them in place