Copying and changing is always a difficult issue, many CDs and DVDs can be dealt with directly, but many have copying locks and restrictions, and they should be respected - who wants to work without a pay?
I've used MagicISO to create images of games, in order to save my discs. Just about all I can say. The differences are millimetric, all that counts is the result. I'm not the EXTENSIVE user, just thought I give a point of view.