you can either choose to hyper-specialize and become the best in the world (top 1%) at doing one very specific thing, or you can try to become very good (top 25%) in as many different areas as possible, which you then can use in combination.
In short, prefer the generalist over specialist approach. Now, from the MBA perspective, management is a skill which can be taught to any graduate-therefore the generalist approach works. For the headline making jobs(consulting, investment banking etc), prior specialist experience is rarely counted, atleast on an Indian campus. Still, let me try to state the pros and cons of each as objectively as possible. Pros are
- Uncertainty:-One never knows whether the chosen career will go boom or kaput. Think of a person who studied till 2009 to become a prop trader. What would s(he) do once the desks are shut down post Basel III? Hence, the importance of multiple areas.
- Unlearn and relearn:-The pace of change(local, regional, national, global) is so much that often the very basic mental models need to be reexamined periodically. And some old skill sets/requirements may just become obsolete/destroyed. For example, real estate agents/human travel agents are going that way due to the internet. So those with realistic other career options can unlearn and relearn with a more secure feeling.
- Multi task & network:-Combining multiple skills gives a good synergy(hopefully!) and also allows getting the best from various fields. For example, Indian finance professionals in the corporate world often have multiple credentials(MBA+CFA), (CA+CS/CWA) to signal their knowledge/mastery of multiple fields. And it does help in terms of membership and reach
- Contrary to the increasingly specific Googlized world:-Customization, specific search results etc have spoilt the generation brought up on a diet of getting exactly what they wanted. And a specialist credential fits in that culture.
- Being perceived as less competent:-It is often joked that a Phd teaches the person everything about nothing. However, the significance of a Phd is the social signalling credential in the academic community that the person can withstand the gruelling grind for 4yrs(or more) and have that academic discipline. Even the best teachers(in style/ability) encounter that glass ceiling without a Phd. Similarly, a very competent generalist may not command that same respect from his specialist peers.
- Not being the 'best' in any field:-Being the best needs 10,000 hours or more, as Gladwell puts it. Those who prefer to be good at many things, may not be the best in that. And for those used to being at the top of their game, that would hurt. Also, generalists may not be needed if the organizational culture is to find a near perfect match rather than to bet on someone.