When I went to a new iMac, I had most of my documents on external drives already, so I just had to restore my internal drive files from the Apple Time Machine files from the old computer to the new one, and emails, contacts, preferences, and browser bookmarks all worked on the new machine just like the old one. But my external photo drive is 3TB, so I also have my internal drive and the two external drives backed up on CrashPlan, which has also helped me save files from time to time. And CrashPlan did not need to back up all the files on the new computer as they were already backed up from the old one. "Suspenders and a belt"