I attended a couple of the social events last year, and was unable to attend others. I got the impression that they were really designed to help you, the applicant, get a better sense of the program without faculty being present. In that sense they were very helpful, because it was nice to interact with residents outside of work and to get their uncensored impressions of things. Plus, people are just different outside of work and it is nice to see if you think you would fit in socially at the program. But overall, I did not feel like attending or not made any difference in the final match outcome. Of course, if you went to a dinner, got drunk, or made a really bad impression somehow, it could probably hurt you. But I did not see anyone doing that. Hope that helps, good luck.