Time Machine works by backing up every file on your Mac—including things like applications and preferences—to an external hard drive. The only thing not backed up is the operating system. If anything happens to your Mac, you can go back to the copy stored in Time Machine.
Tip: Time Machine stores hourly backups for twenty-four hours, daily backups for a month and weekly backups indefinitely, limited only by the capacity of the storage being used.
Time to try it, after finally got a free external HD.