How will a full hard drive affect my computers performance.?

All you need is e few gigs free for your computer to run normal. what makes it run slower is your programs and how many are running simultaneous.delete as many programs you don't need. i very much recommend transferring all your torrent content to an external hard drive. I have an E.H just for torrents. but make sure you buy one that can play your stuff at a god rate cause i didn't :( . some e.h are made just for certain files, only mac compatible, etc. so do a little research before buying. Cheers!