With external hard drives being much more affordable, I now unload most files that I am not immediately using on to an external drive and only keep current files on the computer's own hard drive. That way you can ensure you have adequate space on your internal hard drive.

I also have a completely separate disk for the originals of media files - pictures, audio, video and load the originals from my camera, camcorder and audio recorder directly on to it and then import the files I want to work on to my hard drive.

My internal hard drive is 250GB and has just 68 GB on it - both programs and data but I have 270 GB of data on a 500 GB external hard drive. Admittedly much of the stuff on the external hard drive is duplicates but the size of the task of sorting it and the risk of losing an important file means that it is not worth pruning. I was recently able to recover some files that I thought I had lost so not deleting stuff on the external drive proved its worth.