Backups & restore points · Time Machine and backup strategy
Which folders should I back up?
Short answer: Anything you couldn't recreate — Documents, Desktop, Pictures and your photo library, project folders, and what you've moved to your fast drive. Apps, caches and re-downloadable files usually don't need it.
Back up anything you couldn't recreate: usually Documents, Desktop, Pictures and your photo library, project and work folders, and anything you've moved to your fast drive (the built-in Fast drive working set covers that).
You usually don't need to back up apps (you can reinstall them), caches, or Downloads you can fetch again — Data Backup already skips caches and temporary files by default. Start with the irreplaceable, then add more sets as you go.