Most online applications don't ask for or accommodate a cover letter, which has led to the mistaken assumption that cover letters are no longer a necessary job search tool. When you're networking with humans, they can often send you a job description. You can then write a persuasive and compelling cover letter that very specifically sells your fit for the job. During my decade as a recruiter, many smart and accomplished women sent me a cover letter that was nothing more than one dashed-off paragraph they also sent verbatim to every other employer and recruiter as they put their hats in the ring for virtually any job.
This paragraph was basically a very generic "I'm qualified for this job; please consider me". There was no sales pitch or proof that they were actually qualified. The cursory cover notes also gave me zero motivation to learn more about the candidates: they essentially were asking me to do a lot of work to figure out if and why they should be on my short list of candidates. I viewed these candidates as apathetic and unwilling to go the extra mile—and they were relegated to the bottom of the pile.
Recruiters and hiring managers to have hundreds—and sometimes thousands—of cover letters and resumes that are sent to them for just one position. It's not humanly possible to read them all. Recruiters sift through candidate materials quickly—stopping only when someone makes a clear and strong case about their fit for the job. The formula for making that strong case is pretty easy and straightforward. You don't have to come up with clever wording, a unique format, or a long list of general achievements. You simply have to read the job description carefully and address all the required skills, experience, and responsibilities. Recruiters and hiring managers want to get as close as possible to their ideal candidates. The more you show them that you have the skills and experience they want, the faster you get on the short list of desirable candidates. It's as simple as that: a point-by-point match-up of your skills and experience with the requirements of the job...a cover letter that essentially says, over and over again, "I'm a fit", "I'm a fit", "I'm a fit". When you do this point-by-point match-up, a cover letter for Job A will never be an exact replica of a cover letter for Job B. But what if you don't have all the skills and experience listed in the job description? Then you have to think carefully about whether it makes sense to present yourself as a candidate. You should meet at least 75% of the major requirements to be considered a possible candidate. You can always talk about comparable skills and experience for a few requirements you don't meet—but it's a very rare case that employers overlook a large percentage of the criteria they want to see in an ideal candidate for the job.