Some schools may want to prevent appointments made on the current day from being modified, by staff or students. You can essentially 'freeze' appointments made for the current date. This is useful to many schools that don't want students or teacher making last minute changes to the schedule. Once the current day's appointments are made, they want them to stay that way.
To use the 'Freeze Appointments' feature, you will need to enable it, as a site admin. Logged in as an admin, go to Admin in the navigation, go down to the General Settings box and select Configuration. There you will find a section entitled Freeze Appointments. By checking the box, you will make staff and students unable to modify the current days appointments. Unchecking the box will automatically undo that action.
When this box is checked, staffers can still schedule students, and students can still schedule themselves, when the schedule is open. However, once an appointment has been made, it cannot be changed. For example, if a staff member scheduled a currently unscheduled student for the current day, that appointment would be 'frozen.' That staff member, or another staff member, would not be able to modify the appointment. If a user tries to schedule an appointment, they will get this error message.
Similarly, even if a student is enabled to self schedule, they wouldn't be able to modify the appointment. This is the case even if the student self-scheduled into that appointment.
For both staff and students, 'freezing' appointments can help keep things consistent within the school day, and ensure that everyone knows where they need to be during flex time.