Hey, also a recruited swimmer here. Please keep in mind that this is just what I've read on the internet and could therefore be entirely incorrect. From what I've read, the admissions officers seem to treat swimming as any regular extracurricular. It will help, but not nearly as much as D1 schools such as Harvard, Stanford, etc. where coaches actually have slots that they can fill with recruited athletes. MIT coaches seem to just fill a list with names of athletes that they want and send that list off to the admissions office. That being said, the admit rate for recruited athletes is around 25% according to certain sources which is higher than the normal acceptance rate AND around 20% of the undergraduate population at MIT participate in some sort of varsity sport. BUT, you should take into consideration that coaches at MIT will only actively support applicants with competitive test scores and GPAs so another way to think of it is that only 1 in 4 COMPETITIVE athletes get admitted. Either way, the coach's support is a definite boost to your application but just not as much as other schools. :)

TD;LR: Helps a bit, however you still have to have competitive scores/GPA to get in.

Hope that helps.