Top scores provide a broader picture of your abilities, making you more competitive. Factors like GPA, difficulty of course load, and test scores are weighted with greatest consideration.
If you can do well on the ACT or SAT, you should take it. If you don’t achieve a good score, you don’t have to submit it, but if you do, it will make you a stronger applicant. For some, it might make sense to submit scores to some schools but not to others, depending on how your scores compare to those of recently admitted students.