A well written cover letter can make the difference between receiving an invitation for a job interview or being passed on for another applicant. First impression counts and a cover letter is a way of introducing yourself to an employer.
A well-written CV is your VIP ticket to the interviews. Nowadays the recruiters have to scan dozens of CVs before they decide who to invite to an interview. So it is likely you will have only a few seconds to impress them with your competence and experience. Make those seconds count.