Practice makes perfect. Think back to when you were first learning your multiplication tables. Your elementary school teacher probably had the whole class recite each times table until you had them memorized. Study periods give you the opportunity to look over your notes regularly, so that studying for a test is a quick review, not a monumental task. Get more done.
Most students limit their study time to completing homework assignments.
We're not knocking that - it's certainly important to do your homework. But on a light homework day, you could get a lot more done. Let's say you've set aside 2 hours to study on a given evening, and your homework only takes 45 minutes. You could use the remaining hour and 15 minutes to work on a major report or to review the day's notes. Your workload later in the semester will be lighter, when you'll probably need and appreciate the extra time.