You might wish to drop the lowest grade out of a group of grade items, say the lowest quiz grade out of a set of 9 quizzes. You can set up your gradebook so that this is done automatically for each student, as long as these conditions are met:
1. You must have your applicable items in a category.
2. All items must have the same weight/max points.
3. You cannot have an extra credit item in the category.