Mac storage basics · Erasing, encryption and selling a Mac
What is FileVault, and does it slow down my Mac or use space?
Short answer: FileVault encrypts your startup disk, unlocked by your login password or recovery key. On modern Macs it has no noticeable speed or storage cost; keep the recovery key safe.
FileVault encrypts your startup disk so its contents can't be read without your login password or recovery key. Turn it on in System Settings → Privacy & Security → FileVault.
On modern Macs it has no noticeable speed cost and doesn't use extra storage. Keep the recovery key safe — if you forget your password and lose the key, your data can't be recovered.