Online Booking is completely optional in GoReminders. If you don't want your clients to book their own appointments, that's fine! You don't need to set up the Booking Form in your GoReminders settings.
For example, if you're looking for a scheduler that sends out a confirmation when an appointment is made and a reminder the day before the appointment, but you don't want clients to be able to schedule their own appointments, you can still use GoReminders for all that.
To send out reminders to your clients, just create your appointments under the New tab or on the GoReminders calendar in any view. The reminder messages will then be sent out according to the Reminder Schedule set up in your Reminder settings.