I agree with Michael that the spin bikes should only be used under supervision, for both safety and liability reasons. But to allow access to other areas in your gym, as Harris suggests encourages activity and keeps the clients a part of your facility. It goes without saying that you need to make sure that your liability insurance adequately covers you when clients (and staff) use equipment unsupervised.
I used to work for a small personal training studio, which offered only personal training. But for those clients who were still using personal training sessions, the studio was available to them so they could use the bikes, treadmills and elliptical machines even when it wasn’t their day to train. I think it was a great way to keep them active and keeping them from joining another gym just so they could use those machines.
I know I am a little late in this discussion but I thought I would still add to it. I manage a small government facility, we have 300+ members, and they often inquire about using the indoor cycle bikes outside of class settings, and we do not permit it. 1. Most people naturally prefer to cycle at a high cadence with no resistance, to set up there seat where they have more than a 30 degree bend in there knee, and to ride in a hunched over position…which are all indications for bad injuries. 2. Indoor cycle bikes are not as durable as a treadmill or upright bike. Ongoing repairs to maintain them from improper use alone will dig into your maintenance budget. I usually explain that the indoor cycling bikes were not designed to be use outside of a class setting. An instructor needs to be present to make sure that you are properly set up on the bike, and spinning at acceptable cadence and resistance to ensure that there is no risk for injury.