this question relates to the origin and different educational philosophy across the world. in practice, there are many half year, one year and 18 month mba programs in europe, while recently more and more b schools in america start to introduce one year mba programs. many european scholars believe two year mba is just a waste of time if you are only to enhance your skills in your speciality or to modify your career path. on the other hand, americans pride in their creative transforming career through mba education so that two year seems necessary. however, few instances of successful professional transformation are cited by b schools' recruit ads. more often than not, they may alter your career path. for most b schools, they prefer the applicants are passionate about continuing or extending their status quo in career, which means less work for the school but more rewards upon graduation, both for schools and the applicants.
whether it's worth or not largely depends on your individual situations. actually, little difference is found in the studying time between two year and one year mba: the former 16 months of study while the latter 12 month with more specilized focuses on certain majors. also you need to make a double take on your purpose and future goals after mba. mba just doesn't gild much on your professional expertise, but it does glitter your name as well possiblly your reputation in the firm.
so, make your decision discreetly, but one year or two year mba per se is not the point.