How do sitcom stages work?

I recently watched the 30th anniversary special of Everybody Loves Raymond and it made me wonder how sitcom stages work. I've seen what it looks like from the audience but the special was recorded on the same stage the show was recorded on and it looked exactly the same all these years later. When a set is no longer in use does it stay assembled and decorated and just stored somewhere? I know there are shows that share sets so I can't see that being plausible. Someone please explain - I'm so intrigued!