With the subtotals, you can keep an eye on your grade's "dynamical" state and see how it evolves over time.
SIDE NOTE:
Some of you might see a number in parentheses. In our grade book, if at least one row referenced in the formula for the calculated subtotal has a value, a running total appears.
For example: with a formula that calculates the sum of the HW88 and HW202 scores, if there is a value in the HW88 row, e.g., 12, but not the HW202 row, the HW88 value appears as a running total, (12).
Running totals are italicized and appear in parenthesis.
After there is a value in the HW202 row, e.g., 3, the formula is completed and appears in plain text like other grade book entries, a plain old 15.