The purpose of a standard allotment is to reserve slots for user of a special participant group.
Example: Event date group with 20 slots, standard allotment: participant group OU, number 10. The event date group has 20 slots. Via the generated standard allotment 10 slots are reserved for users with the appropriate OU. These 10 slots can only be booked by users with the appropriate OU. All course participants can book the further 10 slots.