As a kid, my dad always insisted on a tarp under the tent. I never much thought about pitching a tent without footprint of some kind.
If I thought about my reasoning, now, I guess it's not to preserve wear-and-tear on the tent but to keep moisture from wicking up through the bottom of the tent. So, if my tent's floor is waterproof, then I might rethink using a footprint of any kind. Hmmmmm.