iMatch is only for music.
It compares your iTunes library with its own library to see if any of your tracks are already in its library.
If it does not find a match, it uploads the track from your library.
Not very good as a space maker.
Why now purchase another external hard drive, to go with the one you use for your Time Machine backup hard drive, and move some of your music, videos and photos to it?
More on iMatch here: http://www.idownloadblog.com/2011/11/14/itunes-match-the-complete-walkthrough/