Are you using Microsoft Windows?
If so, I would definintely recommend a second HD. My experience shows that Windows is much more stable running on a special harddisk. You can also just format the Windows HD, if it's getting out of hand, without endangering your audio data. Another good reason could be to use a new harddrive for audio, everytime the other one's full. Harddisk aren't that expensive these days, so regard it simply as a data storage.
david