Owners/Managers can require at least 1 valid email address when employees book a tee time for a golfer on the tee sheet (if they call in or are in the pro shop).
If they are making a booking for a foursome, they will need only 1 email address on the reservation in order to save it.
Settings > Tee Sheet > Email Required
As demonstrated below, the reservation cannot be saved before this action has been completed:
(click on the gif to enlarge)