I just wanted to post this because I have seen quite a few profiles of kids from upper middle class backgrounds, with top grades and scores applying to the ivies and other elites without having taken the subject tests because they think they are optional.
The subject tests are not really optional for such kids. The tests are truly optional only for kids from low income, very underprivileged backgrounds.
If you come from a middle class or above background and want to have a decent chance at these types of schools, please do not neglect to take subject tests.