Little ones I tend to leave alone.
Bigger ones I might leave alone, especially if they keep their distance.
Big ones? ....No guarantee of anything.
I can't say anything about my cat leaving them alone, though. :P
Though thankfully most of the bigger ones here tend to stay outside (my windows are at ground level here, so it's easy enough for spiders and other things to crawl in), and all I've seen recently are little tiny ones that I don't even bother with.
Oh, and if they decide to hang from the ceiling and say hi (that has happened to me once), they're probably getting squashed if I can find them again. Assuming I haven't already run away from the spot and refused to go back there at all. There was much flailing that night on my end.