Not required. I wouldn't bother but...
Possible reasons, things to consider:
1. You are applying to civilian college that REQUIRES it.
2. You might need a "confirming" score to balance a bad grade, low test score, and/or failing AP score, or uncertain rigor school where you want one more national score to confirm subject mastery.
3. You can score 750-800 .
4. Select English, Math 2, Chem and/or Phys. Foreign language or any other only if a strategic reason or you are taking that 3rd test same day.
Also double check if your school offers free codes, especially if you get free SAT/ACT in addition to the school-based freebies. My older DD got 2 free subject test days, which was 2 x 3 exams, not just 2 exams. What a deal! But she had to know about it and ask to get the codes.
My opinion:
Most will take a subject test in the Spring after junior year course. I would skip subject tests and focus on SAT/ACT instead. Get your high scores there, not on subject tests. Parameters on my DDs - you guys aren't applying to any schools that require subject tests. SAs, or State U and/or U of State!