With Invitations, you can have a client schedule a date (or as many dates as you'd like) while booking you. You can have a user schedule a Shoot Date, or a Viewing Appointment right when they're booking.
To do this, you'll need to add your Invitation to your Booking Proposal or Booking Page. To do this, go into your Booking Proposal or Page. Click the "+ Add Invitation" button in the bottom right corner.
You can choose either "Schedule the Shoot Date" to have your client specify the Shoot Date, or you can choose "Attach New Invitation" to have your client pick a new date. This would be used for adding a new appointment when a client is booking.