Do I need to delete a room?

No. It can be reopened at any time with the same name. The chat and the shared document will disappear from the room, however, when the last person leaves it (unless you copy the Share link of the board beforehand). A conference room is created anew when the first person enters it. In the browser and in the app, those rooms are displayed that you have previously visited (this information is not stored on the server, but only locally on the device – you can delete all of them by clearing the page cache in your browser).