I read somewhere that some people tell you not to bother with the cover letter. Which is surprising, because that's the only place where you write why you want the job.
Generally, in my field a good cover letter can get you an interview when your resume may not do the trick by itself. I had an interview a while back and it seemed to me that they were looking for someone way more experienced than myself (which they were). So afterward I asked one of the interviewers (a woman I have interviewed with in the past) why they interviewed me if they knew I didn't have the experience they wanted. She said my cover letter added context to the experience I did have more than other more experienced candidates.
