Very very few colleges recommend/require Subject Tests, and those that do state so on the websites. Generally, Subject Tests fall into 4 categories in the admissions process.
• Required
• Recommended
• Considered
• None of the above.
Required is self-explanatory. Recommended is what is discussed on this thread. Considered is truly optional - if the scores are great, it can help and certainly won’t hurt.
Almost all publics (except as examples top UC’s and UGA don’t consider them and do not want them). Many LAC’s (but not all) will consider them. If your kid’s list does not have schools that require/request, then don’t worry about it.
Not that even for colleges that do not require/recommend Subject Tests, there are some uses. As an example, if the colleges has a foreign language requirement for graduation, a high enough score on the Subject Test may exempt them from the requirement. Of course, that colleges generally also have free placement test which accomplish the same thing.