4 stories here, all from the 90's and all from the central Oregon coast in state and NF campgrounds.
1) My parent's ice chest disappeared overnight along with a few others in the same campground. They found theirs dumped nearby along with the meat and soft drinks that were in it. Obviously teens looking for booze, finding none there.
2) While tent camping we locked everything up at night except the lantern which we set on the mat just outside the tent door. Woke up to it missing (with 5 college guys inside the tent). Same campground as #1 but different trip.
3) My brother left his ez-up in the bag on the table to save the spot while we drove away for a bit. Our cousin left an axe, lawn chair and car battery in his site. Everything was gone when we came back. The funny thing was the ez-up was beat up and had turned inside out a couple of times before from filling up with rain. It was not much of a prize. Even better was the battery was stone dead and useless.
4) While we were sitting by the fire our neighbors caught someone underneath their ATV trying to steal parts while they were 20' away at their fire! The guy managed to unbolt one end of the tie-rod. They saw him as he ran off when he got spooked and they didn't discover the attempted theft until later.
So yeah, if I care about it or the trip would suffer without it, I lock it up or put it away.