I just setup a brand new iMac for home. I've never had a "shared" computer in my home so this is a first for me... I connected a external firewire 800 HD for Time Machine backups and I've set it up ...
Periodically backing up your computer is always a good idea. You want to make sure your documents, photos, and files are protected in case of hardware failure, software glitches, or malware attacks.