If you're working in a basic science department, already have strong research experience, are a good applicant for the school (grades, etc.), and want to do an MD/PhD then it can help quite a bit.
If you're just doing the experience for a standard resume slot then it can help if you get to know the school environment well and talk to different people. That way you can mention on the secondaries or during the interview that you really like X about the school, have spoken to students Y and Z, know that R does great research, etc. All of that is assuming you're still a good applicant for the school.
Just doing a program for the sake of possibly getting a little boost is probably not worth it.