I'll try to build on tacit's post (the easy way)...
Unless you, yourself, have set custom permissions, the correct permissions for every folder and file in your home folder are "pre-ordained" when you install OS X; therefore, out-of-whack permissions can be readily and accurately detected and corrected.
tacit has described one way in which home folder permissions get o-o-w, and while I'm not up on the details of how it happens in other instances, I do remember at least a few posts over the years that dealt with users losing ownership of stuff within their home folders. (I suggested repairing perms because I think I remember incorrect home folder perms being at the root of the "immediately deleted trash" problem. [I searched, but fruitlessly.])
Hope that helps.
