Of course but if you don't have a bike but you do have a membership, it can be a great workout. Especially if you have family and time is a factor, one hour on the stationary with an instructor pushing you can still give you great results
Incase you haven't seen some of les's previous threads the guy is an animal! He teaches a couple spin classes then jumps on his bicycle rides a couple miles home. Cooks himself a very strict meal jumps back on his bicycle rides back to meet another client and goes for a couple more hours. It was before last hunting season I believe he had a blog on a thread about his "normal" day. I hot tired reading it!