I feel like this might be somewhat common for athletic recruits, but what about non recruits?
Does Penn require subject tests? If so no acceptance without them. If they are recommended and not submitted then the res of your application needs to be exceptional.
Has it happened? Probably. Was the applicant exceptional in other ways that negated the need for a subject test? Definitely.
I submitted my application ED without subject tests (I submitted my ACT), that said…the nearest SAT test center for me is 1 and 1/2 hours away
Per their website:
SAT Subject Tests are recommended but not required. Applicants who do not take SAT Subject Tests will not be at a disadvantage in the admissions process.
If you can submit two solid SAT subject tests, it will be beneficial. Subject tests are additional information about the student that is helpful to the admissions office. I am sure they don’t deduct points for not submitting them, but it is a missed opportunity to strengthen your application.
I concur with @Much2learn. It is beneficial and will help you. For example, Wharton recommends Math II. If you can demonstrate that you are strong on math in your application, like, advanced math courses, contests, etc. You do not need to send SAT Math II.
On the contrary, If they look through your application, and think that you may be weak on Math. A strong score on Math II will boost your chance.