There's really a strong reason to do this for things like user session tokens, where using crypto and avoiding database updates could easily remove a substantial portion of your database traffic.

But for things that are less common, like password resets and email validation, consider the downsides:

a) using the database gives you a built in (depending on schema) audit log of these events, where a signed token does not b) If the key is stolen in the scheme described, the person in possession of the key can hack into all your accounts. If you use database state, someone needs to have access to the database. c) (also mentioned above) You will almost certainly be able to have a smaller token if it refers to database state, which has it's own advantages: copy and paste errors, etc

There's certainly advantages to crypto tokens/cookies, and they're the right call in some circumstances, but there's downsides to consider as well.