As long as I've been running spinning classes the biggest challenge, for me, has been managing the attendee numbers. Issues range from the standard drop out rate just before the class, to manually handling the waiting list.
Ever since I switched to organising my classes using I'm In, I've found I've had to pick up the phone a lot less as the automatic emails and waiting list handling do all the heavy lifting for me.
The one thing I wasn't expecting is that the usual drop out rate has declined considerably. It seems that the big "I'm In" button on the email has a psychological impact on people, and when they say they are coming, they really do come along.
As my classes all run at set times each week, I can just use the recurring event functionality to automatically send out all of the invites week after week. It's honestly saving me so much time and stress!