What's a good comparison?
How about, "A resume without a cover letter is like a brownie without ice cream." It's nice, but it could be a lot better with very little effort.
Colleges and career counselors focus a lot on why you should have a great resume, but they rarely even hint that without a cover letter, the resume has very little impact.
Maybe they take that approach because so many jobs that are advertised online simply ask candidates to upload their resumes, with no provision for a cover letter. However, as a recruiter, I can tell you that at least 80% of all jobs are never advertised, online or otherwise. Companies just do not want to deal with the onslaught of resumes from candidates who are not qualified and do not meet the basic job requirements. In many cases, finding great candidates for those jobs is contracted out to a recruiter. Whether you are working with a recruiter or dealing directly with the hiring authority, you will do yourself a huge favor if you include a great cover letter with your resume.
Why is it so important? There are several reasons. First, it allows a bit of your personality to show through your writing. People who read these resumes are no different than anyone else in that they like to get at least some idea of how the person represented by the resume connects with other people. A cover letter lets a little bit of your personality come through, and that is always an advantage.
Second, it gives you the opportunity to do a little pre-selling. A good cover letter inspires the reader to continue on and to read the resume. It allows you to express why you are interested in the job, whereas the resume itself expresses how you are qualified.
Third...and especially important if you are pursuing a job that will require you to communicate effectively within and perhaps outside the organization...it shows that you know how to write a letter and that you have basic communication skills. The more "unknowns" you can answer with your resume and cover letter, the greater your advantage in getting the interview you want.
If you are not skilled in writing and do not feel comfortable creating the cover letter (and if the job you are seeking does not require this skill), hire a professional or get someone you know who is a good writer to help you with the cover letter.
It does not take much time to write a good one, and the payoff can be considerable.
Ken Murdock is the owner of Murdock and Associates Recruiters and New Wave Resumes, and the author of . He recruits top talent in sales, project management, accounting/finance, manufacturing operations, and engineering for the manufacturing sector, oil & gas, and construction industries. New Wave Résumés offers professional résumés and interview coaching for executives, mid-level professionals, recent graduates, and anyone seeking to take their skills and talents to a higher level.