Why do I need pvc if I am using database?

Hi, this may be a stupid question, but I need some clarity.

I am trying to launch grafana on kubernetes using helm chart. If I am using a postgres database to store my grafana dashboards and users why do I need to enable persistence(using pvc or statefulset)?

What kind of data is stored in the pvc? If the data is only plugins, then I think plugins will be installed each time a pod is restarted. So, it is not exactly lost on restart, right?

please can anyone explain? thank you.