Why, that is their area of expertise and unless you are going to bring yourself to their level of education in their field of expertise then you should rely on them. Especially accounting and major legal situations. Missing a detail on either of those could cost you far more than it is worth. Law and accounting are the two disciplines I specifically advise people to cover first when getting out on their own.

As for the MBA, if you are on your own then numbers don't add up. You can get the education for free so why would you pay for it if a piece of paper is not going to affect you bottom line. As well, there are serious concerns that formal documented education outside of some specific disciplines may have past it's golden age (in relation to job qualifications). The market is hyper inflated due to lending practices so the numbers are really bad on a degree for a degrees sake.