This would be for the schools you have not been admitted to yet? It would likely not make a difference unless they specifically request such a letter from applicants.
Yes -- there would be no reason to send them if he had already been admitted!
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To me it looks like he is saying that he had two IIs at schools that are not his dream schools, but are schools he'd be happy to attend. Given the late hour and the fact that he hasn't heard from a bunch of schools, he's asking whether now would be a good time to send a LOI to one (or both???) of the schools where he interviewed.
FWIW as a future applicant, I agree with the advice already given (e.g., at this point in the cycle with zero As, such a letter would look more desperate than anything else, and is unlikely to produce the desired result).
OP - based on my observations from previous cycles, such letters are most effective later in the cycle, after you have at least one A and are trying to provoke a preferred school to pull you off the WL. Until then, you not only have zero leverage to use in sending such a letter, but you haven't even established that they have any interest in you post interview. On the other hand, it might be totally unnecessary, because they might have already decided to send you an A!
As tough as it is, the only thing to do at this point is to sit tight and wait. Look at it like this -- if they have already decided to reject you, sending a LOI is not going to change that. If you are getting an A, it's unnecessary. And, if you are going on the WL, you'll have plenty of time to send the LOI between the time you are notified and when they start pulling from the WL. Sound reasonable??? GOOD LUCK!!!!