The biggest collection of lost files for me is associated with Mail, and I don't see any way to rease content other than deleting messages. BTW, it was quite a bother to erase Sent messages since I didn't see a way to delete them all as one can do for Trash.
"Erase all Content and Settings" does sound somewhat easier than a full reinstall, though it sounds like all preferences and email accounts would have to be set up again. It seems like there should be a simpler way to delete a program's data. Normall I would try "Erase all Content and Settings", but it looks like we are all getting new phones so I'm more interested in finding out whether this sloppy file handling is present in both iOS and Android, because if Android is significantly better I might switch so as not to have to erase all my settings from time to time to keep the phone from getting overloaded. I'd even consider Windows Phone if that was the best solution to this problem.
I would not be surprised if the Mail problem is related to the stuck download progress bug described at https://discussions.apple.com/thread/2528738?start=0&tstart=0, which has been around for at least 3 years, and wasn't even fixed when Steve Jobs was alive so I'm not optimistic that it will get fixed now.