Cover letters are mostly ignored by recruiters, mainly because they're templates and don't tell you anything interesting or useful about the candidate. It takes about 5 seconds to recognize a template, in my experience.
This is also the reason why recruiters scan through resumes. You can scan (but not discern much from) a templated resume in 10 seconds, but you can't read and discern much from a customized resume or cover letter, without reading it attentively. Templates resumes and cover letters don't tell you much about the candidate, other than they know (hopefully) how to copy and paste.
The main benefit of a covering letter is that you can link your strengths to the job vacancy. The resume can't do this well enough, because, hey, we have done a lot of different stuff in our career and we want to showcase our all our versatility. Unfortunately this makes it difficult for the recruiter to decide. This is where a well thought-out cover letter helps. When the recruiter scans the cover letter and realizes that it is not a template, he /she tends to pay more attention and will likely read the resume in more focus.
If the cover letter is well written and draws relevance to the vacancy, then the recruiter is sufficiently interested to read about other areas of the candidate mentioned in the resume. If that is also interesting and bears relevance to the vacancy, there are great chances of the candidate receiving a call for the interview.
Among other services, I also help my clients write their cover letters, resumes and prepare for interviews, based on their strengths. This allows them to showcase their uniqueness from other candidates who use templates, as well as stand a better chance of landing an offer for a job that will satisfy and engage them, while benefiting their employer.
Watch my video "Why you need a Strengths-based Resume" here.
Write to me on ryanbbarretto@hotmail.com if you want to prepare for your next job like this.