I decided to use the above to release more space, and up to a point, it seems very easy to use. But given my general lack of nous about this kind of thing, I'm not at all sure what I'm looking at with the long list of items that come up on the sweep, and which ones I can safely delete. "Library", "Applications" etc. seem self-explanatory (and I assume I don't touch those) but there are lots of others about which I know nothing at all. How does one tell which items are redundant/useless and can be safely deleted to release disc space?