I use egg crate in my tanks, and I love it. Cause without it, within an hour of adding rock to my 125 last year, I'd have crashed it through the bottom when a rock slipped out of my hand.
I keep a number of gobies, so rock stability is a major concern for me. I put egg crate down, the the rocks on that, then added sand. It can't hurt to have that little bit of plastic to diffuse at least some of the pressure of a small rock fall, imo.