[michaelt]

Theoretically, if you grade students several times throughout the course, you can correct those who are on course for a poor grade (due to misunderstanding the content, or misunderstanding how much studying they need to do) while there's still time for feedback to improve their grade.

(At my school many teachers were slow to mark and return assignments, so this benefit wasn't really achieved - but it might have been had feedback been more timely)