Also, with my old digital multi-tracker, I only had enough hard drive space for about 30 minutes of 8 track recording. Once that was full, I had to mix and master everything and put it on a mini-disc or some other form of external media (CDR would probably be most common now, but at the time, I didn't have a CDR drive). Once it was mixed, I had to delete it from the internal hard drive and that was it for mixing the track.
With the computer, I can easily pull up a project that I worked on 2 years ago and tweek the mix or redo a vocal track or something. Once my hard drive fills up, I just swap it out with another hard drive and start a new library. If I do want to go back and tweek something on the old drive, I can put it back in the computer and do that.
I've got a 250 gb drive that's full and sitting beside my computer, and I've got a 500 gb drive in my computer that's probably 1/2 full now. Once that's full (probably a year or two from now, depending on how much recording I do between now and then), I'll pick up a new hard drive for $100 and start over, but I've still got all my old projects on the old hard drive.