I've done this a couple of times in the past as I had no other option, I can't say it's really done much apart from fix what was causing me to do it.

@Saturn.

When I installed my 250GB HDD it took about 40-50GB away for it to do it's own thing with. Have you looked in the Game Data Utility. There can be big files in there which aren't needed if you don't play the games anymore. Something like Arkham Asylum or AC Brotherhood are over 3000MB each.