General Manager of macVolks, Inc.
You can back up your system periodically, if that's what you prefer. It's not recommended to leave a portable USB external hard drive connected to your machine all the time. They'll continuously spin, and they don't have any kind of internal ventilation system, so they'll wear out more quickly. However, once Time Machine has been set up for the first time, it will back everything up for you automatically, as long as you remember to plug your external hard drive into your computer every now and then.
Chiara Corsaro
General Manager of macVolks, Inc.Consider having a secondary backup for important files. If you have anything irreplaceable on your hard drive, like your photos, it's a good idea to have another backup, such as on a separate external hard drive, a USB flash drive, a CD or DVD, or a cloud backup.