When you have the "Make a Reservation" or "Suggest an Event" template turned on in multiple calendars in your account, you'll see that there's an option to choose what calendars you book your event to. Any calendars that have "Make a Reservation" turned on will be listed in the "Choose One" drop-down list for your "Make a Reservation" form and the same applies to any calendars with the "Suggest an Event" template turned on. See the image below:

When you have "Make a Reservation" or "Suggest an Event" turned on in multiple calendars, there may be calendars that you don't want to appear in this "Choose" drop-down menu. There is a feature called "Do not list this calendar in 'Self-Book' forms" that you can turn on in your calendars to prevent that calendar from showing up in this drop-down menu. 

This feature is especially useful if you have a master calendar with multiple calendar overlays. Turning on this feature would allow visitors to pull up the Self-Book form from your master calendar, but they wouldn't be able to save that booking to your master calendar and instead choose the appropriate calendar that the booking should be saved to.

To turn the "Do not list this calendar in 'Self-Book' forms" feature follow the steps in the image below: