None.
There has never been a time, and there never will be a time, when I will keep a single file there for more than a few days. Even then, it only contains one file at a time if it has to.
Normally, whenever I delete a file, the next thing that I do right after that is to go to the recycle bin and permanently delete it.
Yeah, I do this because for some reason, I feel really, really disturbed when I see the recycle bin as full, specially since I feel some kind of peace once I see things perfectly. You could say I'm kind of a perfectionist.