Well, in the current context, deleting stuff that could be used against you in a lawsuit. Doesn't need to be something you did that was wrong but maybe just something you wrote that expressed doubts about a strategy, for example.

But there's also just cleaning out all the cruft which makes finding useful stuff harder. Since going all-in on Gmail, I delete far less than I used to and that's not entirely a bad thing but I also have to sift through a lot more stuff when I'm looking for something.