What distribution do you use? I haven't heard of a bin-folder inside a user's $HOME in any distro for a long time...anyway, I'd guess "bin" has the same meaning as /bin and /usr/bin - put binaries, program executables in there. no idea what it's for in $HOME but that's the best guess I can think of
Documents are for documents I guess..but what distribution do you use? How new is it?