with this setup, Vault will create a new database user based on the configuration you set (read-only for some services, for example), and will attach a time-to-live to those credentials; as long as the application is using them, it will renew the TTL. When an application is killed, or scaling happens, etc, and the application instance isn't using those specific credentials, Vault will clean up and remove the unused account cleanly

Can do all sorts of great things with this; for example TLS (ssl) certificate renewals, etc, as the certificate expiry IS the TTL; when a certificate needs to be renewed it can happen automatically and your application can receive any signal you choose (SIGHUP, for example)