I’m certainly not advocating that the Yale/Harvard system is perfect; it’s not. Without preregistration, it’s incumbent upon the department/instructor to project enrollment by course (and thus, resources needed), which is usually OK for courses that have been offered before. However, at least for Harvard, they have a tendency, particularly in humanities/social sciences, to offer courses once, and they are never seen again. Every semester there are stories of courses that enrollment far exceeded projections, which leads to scrambling for classroom space, finding more TA’s etc.
I would also suggest that what a college has to do to make registration more efficient and/or more flexible is different when a school has 1600 students per class vs. 6000.