They can be helpful if you have services that need to call other services on behalf of a user request.
For instance, user A calls Product service for Product information but that response also includes Recommended Products and Advertisements from those two services. Product service can pass the JWT from the client to Recommended Products and Advertisements which removes the need to establish trust between those internal services (since authentication and authorization info are just passed around from what the client provided).
You can also use them in federated auth schemes where the issuing system is separate from the recipient. I think the use cases are pretty similar to SAML for this type of system but with a smaller "auth token" size.
Just because you're accessing a database on a request doesn't mean you're accessing the database that stores the authorization and authentication info.
For instance, user A calls Product service for Product information but that response also includes Recommended Products and Advertisements from those two services. Product service can pass the JWT from the client to Recommended Products and Advertisements which removes the need to establish trust between those internal services (since authentication and authorization info are just passed around from what the client provided).
You can also use them in federated auth schemes where the issuing system is separate from the recipient. I think the use cases are pretty similar to SAML for this type of system but with a smaller "auth token" size.
Just because you're accessing a database on a request doesn't mean you're accessing the database that stores the authorization and authentication info.