Do you need to back up all your movies and music? Either it is all ripped from discs you still have or is pirate and can be downloaded again.
Not everything pirated can be easily downloaded again. There are lots of torrents that only have a single seeder, who might disappear halfway through your download. Often it is hard to find the content in a lossless format -- most films can be had from The Pirate Bay, but only as <1GB
So, backup what you get, because you might not ever see it again.