If you are shaking hands with the hiring manager, you are introducing yourself verbally and requesting an interview. In this case, hand them your resume without a cover letter. On the other hand, if you are sending a resume by mail, if you give your resume to a friend to hand in, or if you leave your resume with the hiring manager's secretary then you are not shaking the hiring manager's hand and you need to have a cover letter enclosed with your resume. Brief and Simple Hiring managers only glance at cover letters. I recommend letters be 3-4 paragraphs.
Many people provide lengthy autobiographies in the cover letter.
They regurgitate their resume and then some. This is a waste the writer's and reader's time. Cover Letter Content Address these 4 topics in a succinct manner and the hiring manager will be grateful. You can obtain examples of a few excellent cover letters that will make letter writing simple, by clicking to the Cover Letter Example section.