How often, and how much? Decide by thinking through how you would use your backup to restore your Mac after disaster.
An overview of some of the many ways of keeping folders in sync, backing up, and making remote copies.
Do third-party disk tools work with Fusion Drives, or are you stuck with just Disk Utility?
How did some of my old disks and folders get to have ‘custom access’, and how can I fix that?
How many bytes are there in a kilobyte, and have you heard of a kibibyte?