Lots of data is in the database This data may include user information, rosters, chatroom configurations, offline messages, etc… It will continue to grow as your users do stuff on the server.
You are probably asking if you should use the embedded database versus an external one? A quick answer is that for testing and very small userbases, the embedded database works just fine. Once you start having hundreds of users, you will want to think about external databases. There isn’t a clearcut number to switch between embedded or external. Users have had good experiences with both.