1st Example: Students who have not been here for some time.
First, click on your Marketing tab and select smart list.
After that, choose the filter desired. In this case, will choose Bookings > Last booking. With this, you can identify students who have not been coming for a while and who do not have reservations about the future.
2nd Example: Students who have been coming frequently but have not been coming for a while.
Add to the previous smart list the following filter to limit this list to people who have booked X sessions in Bookings > Booking number.
3rd Example: Students who came frequently, who have a valid pass but who have not come for a while.
Even more interesting: you can further refine this list by including only those who still have a valid pass or by excluding them in Passes > General.