By experience, I will tell you that is Finance or Economics, Marketing & Communications and Soft Skills that help you be a followed and likable leader.
You might know or will find out that in business, any business, its not about you but about them - your end user, end customer. If you want to succeed build and leverage relationships - it's not about who you know but who knows what you know and do they like you?

Humberto Valle
MBA, Strategist, Investor
www.Unthink.me
https://www.facebook.com/groups/mysmallbusinessresource/
www.facebook.com/iwillunthink
www.twitter.com/officialunthink

You are in classes with highly motivated people which stimulates your intellectual curiosity. You also get perspective which helps you understand multiple industries and markets. Lastly it enhances your crediblity with employers, peers and subordinates.

Network - Completing a healthcare focused MBA connected me with a network of healthcare leaders who I've been able to leverage to learn, advance, and develop in my career. As a physician leader, I didn't have much exposure to pharmaceutical, diagnostic testing, or insurance parts of the healthcare industry. The MBA taught me how these piece fit together and introduced me to leaders in these sectors.

I'm glad I have one. Among other things, it gave me a head start in understanding organizations and how to work with people. When I was in graduate school, I thought the accounting, finance and economics courses would be most important to my future business career. After graduating and gaining more real world experience, I discovered how challenging it can be to reorganize or restructure as a business grows and changes. I wish I had taken more management and organization courses.

I would echo all previous answers, not to be repetitive and add one common reason from my specific experience: creating credibility in new field. When I did my MBA at Queen's University, at the time it was called MBA for Science and Technology. Language is key as it was meant for engineers transitioning to management.

With respect to my peers, a number of them were entering finance, marketing, operations and IT and coming from mechanical, environmental, computer, automotive fields to name a few. The MBA provided credibility to get into the management areas now which may not have not been attainable due to their pure engineering backgrounds.

I see an MBA differently from most people. I think that there is very little to learn in an MBA program that is as essential as humility. The MBA program provides opportunities for you to see that you are not the most qualified at any particular aspect of business. Leaving an MBA program, one should be saying, "If I run a company, I better make sure that all the work is done by my awesome classmates." This humility and self honesty helps a leader to compensate for their failings by hiring the best and brightest and simply overseeing them and directing their excellent work.

Thus, an MBA teaches us to rely on the brilliance of others to achieve great things instead of relying solely on our own abilities.