Finance

In the beginning MBA is a tag that allows you the entry in corporate world and gives you eligibility upvote for decent jobs ( I have seen big companies offering meagre 10k to 15k to fresh MBA candidates, only exception given to selected top B schools like IIM etc. , others are all same for them and candidates accept jobs to either get a brand name of the company or they have limited options)
After few years, you will find yourself at the same platform with colleagues who are not MBA but have equal work experience like you. You might also realise that the specialisation you chose in MBA doesn't interest you as far as that department is concerned at job. For example -MBA finance might have taken that field to become a manager in financial planning in a company but he got an opportunity in areas like Mutual funds, shares, accountancy etc. That time you might realise your MBA is total waste because Finance no more interest you, your work ex in that field will fetch you similar jobs and you would feel that you might have taken marketing. The same situation could be vice versa too
Dual specialisation helps sometime in above scenario but only when you are able to find out your situation in early 23 years of your job. Things get brighten only when you chose a particular field, know what are career options in that field, get a job in that specialisation and that domain, continue working and growing in that profile.