I have a backup partition which I put some files and such on. Basically, whenever my desktop or documents folder gets cluttered, I just move everything to it.
Because it was only my stuff, my account was the only one with any permissions to access it.
I recently decided to set up a domain. I deleted local accounts and made shiny new roaming profiles instead. As such, the owner of the account is now 'unknown' because it no longer exists. So, of course, I want to take ownership with the new domain account.