Since ERAS allows you to send 4, where is the harm in sending an extra one?
what if only some people sent in 4? Would that be "fair" to those who did not? (I dont know the answer, I am just making a point). If they only want to look at three, to make it "even" amongst all their applicants, how should they pick the one to throw out? What is the fourth letter going to get you that the third did not? If you thinkyou have three mediocre letters then one good one will not make up for it. When I was interviewing applicants and reviewing applications it was easy to see what the letter writers thought after the second and certainly after the third letter.
Do whatever you want, but I am telling you that you may hurt (i.e. get screened out) yourself at some places who think you cant even follow instructions on the application.
we would get literally over 350 apps for 3 spots. most of the ones we took seriously all had USMLE over 235 (once you are over that the difference is only a few questions, so to us the difference b/t a 240 and 250 does not matter). A lot(not all) were AOA. Everyone had "interesting" personal statements/stories on why they wanted to go into ortho. An applicant that has a incomplete/erroneus application makes it easy to put in the "no interview pile". It seems dumb and trivial, but we were not/are not the only place to have such screening to get the interviewee pool to a reasonable size. play it safe, just do exactly what they ask for. there is "no harm" in that.