Interviews are different and answers are different but the job role is which you applied for is not going to vary in your life. Job description plays a major role in your selection process, as you go through the vacancy notification in any company you forget to notice the job description as a fresher. Even some times experienced people forget to notice the job description. There are many occasions where I interview a interviewee and I ask about the job description, the candidate some times stand blank on this question or else they just say a different role. This creates a aversion and doubt about the candidate, it makes me to think whether to hire this candidate or not. Since he doesn’t know what he is going to do as when he enters in the company there is no meaning in hiring the candidate. One must always get to know about the job description before he attends an Interview.

There are some circumstances where you really don’t know what the job description is, in case of Campus hiring mostly for technical jobs they don’t mention the job description, but for the non technical jobs they give out the job description. 
In some place when consultants work for recruiting people they just tell the job title not the job description. It is a must to get clarified about the job description.
Why knowing about the job description is so important ??
1) It helps recruiters to screen the candidates easily.
2) If you know the job description clearly your probability of getting selected increases.
3) It helps you pick up the right job which suits your character.
4) It makes you to prepare for your interview. 
Only there are points but the will help you in preparing for the interview. Get to know about the job description or job role very well before you attend an interview that will help you a lot.