My brother just got a Leslie 825 with a rotating speaker from his father in law. He used it when he played concerts with his organ or piano. I don’t know anything about them but I heard some people use them to get a certain sound from the guitar.
Awesome. I used to have a Hammond and leslie years ago. Run guitar through it and it produces a 3 dimensional airy sound that is very cool. I have a pedal that tries to emulate the sound but it can only do so much.