Pros
You get to work out for free at any of the studios. You get 50% off water and socks, but not on the apparel or any other merchandise. The job is really easy. You just check people in, ring up sales, and take inventory and help out with weights during class. After helping out with weights, you have 45 minutes essentially to do whatever.
Cons
The hours can be very early. You need to arrive 30 minutes before your shift, with studios have classes that start at 6:00 am. The pay is low, and there's really no room for advancement. Small class sizes are troublesome--good temporary gig to supplement some income, but don't go into it thinking you'll go anywhere in the company.