We have a small house and don't use ours often, but it has come in handy a few times now that he can sit up and play with toys.
Working outside. Sometimes I can wear him, but gardening and deck work goes much more smoothly when he's in the pack-n-play with mosquito netting over top.
Camping. I typically poke myself in the eye several times when DH and I are erecting the tent. Much easier (and safer) to put a happy babe in the playpen while we do this.
My best friend used to drop her son off with his pack 'n' play when I babysat. Since the babysitters she had were all college kids (we were young), most of us did not have baby-safe homes. We could let her kiddo play and self-feed in the playpen when we needed to attend to dishes or housework or homework. We never let him sit to cry, obviously, but he was often content to play in there, rather than explore our mazes of wires.
I take it when we travel. We pile laundry in it and use it to hang-dry diapers. Very handy.