The School of Medicine has a requirement that a minimum number of preferences must be entered by each student in order to run the application.
Some schools use the N+1 rule, which automatically assigns students “Any Site, Any Course, Any Time Frame” as their last preference. Students entering fewer preferences in an attempt to give the optimizer fewer ways of satisfying them would be at a disadvantage, as their (rule-generated) preferences would include every assignment, whereas another student with more (manual) preferences would have more specific assignments preferences than the “gaming” student.