Studying certain subjects just for your own knowledge is much better than studying just for test scores.
These days, many students cheat on tests and basically get a high score without actually learning anything. Tests don't exactly measure your level of understanding on a certain subject. This depends on a lot of factors, such as how the test was made and how the subject was taught to the students. There could be a test where a teacher made it SO EASY that a student who didn't study could get an A on it, or the other way around.
Studying for your own knowledge is better because you can learn at your own pace. Some teachers make chapter tests occur every week, or some would assign quizzes every single day. That's not good for a student's health, because they'll always have to worry and be anxious about receiving a good grade on all those quizzes and tests. And while they become worried, they can't concentrate, which means they won't be able to get any studying done.
Good test scores aren't nearly as important as actually learning something from studying at your own pace. But hey, that's just my opinion.