It is important to note that RSVPs and check-ins functions are separate - an individual may RSVP in the days leading up to a playgroup, then check in on the day. While the number of RSVPs can be limited, we will never stop someone from being able to check-in on the day.
The RSVP function allows an organiser/facilitator to set a limit to the number of people that can register to attend a session. This may help if you plan on running a big event or if you are getting too many attendees.
The RSVP function is a great way of getting people to ensure they are members before attending a session. It also lets you know who is coming to your session, which can help if new families plan on attending.