The batch is the unit of cost, so it should be the unit of planning
A half-empty batch is a decision you cannot reverse
Once a batch starts, the faculty member and the classroom are committed for the duration. A batch that opened with a third of its seats filled will carry that cost to the end of the course, and merging it later means telling paying students their class is changing, which institutes reasonably avoid. The expensive decision is made before anyone teaches anything.
Confirmed fill, visible while it is still a decision
Holding confirmed enrolments against a proposed batch and watching the fill build turns that decision into arithmetic: open now, delay two weeks, or merge with the adjacent timing. It also shows which timings and which subjects reliably fill, which is the input for next session's timetable rather than a memory of how last year felt.
