I just bought the Seagate 4TB backup drive for my new imac (27" 5K with 2TB). I only have about 500gb on the computer, which I transferred from my old PC. I'm retired, so I won't generate a lot of work files, but I do want to scan and digitize all the old family photos....I guess that may take some space. My question is....Will I want TimeMachine to use the full 4TB of the Seagate to make backups, or should I reformat the Seagate and partition so I can use 1 or 2 TB for regular file storage? In other words, do I need 4TB for endless TimeMachine backups.....or less? What is the normal setup?