One of the most common refrains I hear from applicants is "why do adcoms want us to be clear and specific about our career goals?"
Isn't that what business school is all about? Spending two years figuring out what you want to do. MBA students know that. Adcoms know that. So why is articulating your career goals such an important part of the application?
Put it this way. Every adcom knows that most candidates haven't *decided* on a career path. But they just want you to discuss *one* such path for the purposes of the application -- a path that you would seriously pursue amidst of other alternatives that you may be considering.
In other words, there's a difference between being "clueless" and being "undecided". When most b-school students say "I really don't know what I want to do," they are usually undecided, not clueless. They have an idea of the two or three paths they'd like to pursue -- but they just don't know which path to take (and they have given each path some thought and research). The clueless on the other hand simply don't know anything.
Asking you to articulate your career goals helps the adcom weed out the clueless, with the implicit understanding that you as the applicant may be undecided.
So while it's not really important to have decided on a career path (or to even follow through on what you wrote in your essays), it's important to at least get a clue.
It's important because from the moment you step foot on campus for your first day of classes, the signs of recruiting season for the upcoming summer already begin. The campus will be plastered with more company logos than NASCAR, and more trinkets and swag than an industry convention. Company recruiting presentations begin within the first month or two of school - just as you've barely begun to adjust to student life again. In this kind of environment, it's one thing to be undecided, but it's another to be clueless.
Most importantly, being able to articulate *one* career plan you would like to pursue in your application also reveals a bit about who you are and what you value. Sure, few people know *exactly* what they want in the long-term, but your ability to envison *something* specific at the least shows you have the ability to imagine beyond your immediate reality, while showing that you have some heart and conviction for something (and a plan on getting there) - that you're not just another worker drone who sleepwalks through his/her life.