If you want to cut and edit it or import it into QuickTime-based programs like iMovie or Toast, then the QT MPEG2 component is a great thing to have. However, if you don't need all the power of QT, then there are other, free options available.
If you just want to play the movies, you could use a non-QT-based player like VLC or MPlayer. If you'd like to convert them to something like MPEG4, I recommend ffmpegX or VLC.