This is a great piece of advice from iMore’s Lory Gil. Follow along to make sure you have Apple ID unlock enabled on your Mac. Read through the rest of the post for related how-to info.
Even if you think you’ll never forget your password, this is a smart backup plan.
UPDATE: Looks like this option is moved, or just plain gone from High Sierra. Working with Lory to figure out the new way to do this, check Lory’s post over the next day or so for an update.
UPDATE 2: Turns out the issue is having FileVault enabled, and not specific to High Sierra. If you have FileVault enabled, have a recovery key, you won’t see the checkbox. Yeesh. Bad interface, I think. Better to have the checkbox in both cases, but dim it if FileVault enabled, with some kind of explainer.