When you’re meeting a potential employer for the first time you want to send the right message, just like you would if you were meeting a member of the opposite sex for the first time. Like a first date, if you don’t make the right impression at an interview, you might not get a call back.
After submitting your resume, the first thing that you’re judged on is your appearance. Employers are interested to see the person beneath the cover letter and they’re hoping for good things.