I am a current student at MGH. I know many of my classmates who only attended the online session and still got accepted, so I believe that they are true to their word when they say that it won't negatively affect you to skip the in person session. However, if MGH is one of your top choice schools I would suggest that you attend the in-person info session if it is at all feasible. Being able to speak to current students and faculty and seeing the campus will give you much more insight into the school and the curriculum that you will not get just by watching the online session.