Why do the majority of HR managers want a Cover Letter with a job application?

As reported in Resume Writer's Digest, more than two-thirds of HR managers view a cover letter as a positive advantage for job applicants over competition that chooses to not include a cover letter. There's a catch though: for a cover letter to work in favor of an applicant, it should be well written and personalized to the job that is being applied for. About half of HR managers believe that a properly written cover letter can carry as much weight as a resume. While a good cover letter may not do all of the work in getting an applicant a job, it can go far—and an awful one will most certainly disqualify a candidate.