Pros
The institution has great admin, they will always try to to help you out any way they can. They are pretty large though and you can expect some delays and emails bouncing around a lot. The institute has an awesome brand name and this will help you get your foot in the door or at least get people to read your resume and cover letter. Also there are unparallelled networking opportunities with many brilliant and motivated people, who are generally nice and oftentimes somewhat quirky. being in the middle of the Kendall Cambridge area helps a lot to meet new people and get in touch with the professional scientific and business community
Cons
The biggest negative is the same as in every other academic institution worldwide: you are at the grace of your supervisor, they wield all the power over your career. For most job prospects you require their cover letter and oftentimes their network to even get taken seriously by some employers. This con is obviously not unique to MIT, but despite all their values about student and postdoc right they not actively protect the mentees from their mentors enough, then it is necessary. Overall you are a small part in a big machine and you can get easily lost among the cogs.