I used to think that the cover letter was where I could point to the parts of my resume that were very specific for the job. But I've done more than a few online applications recently that simply didn't have a place for a cover letter.
The cover letter also should be designed to save time for the recruiter. Make space for some very targeted items (name, company, position) so it doesn't look like you are sending exactly the same to every recruiter, but don't make the mistake of spending more than 15 minutes on each letter.
Since you don't know which one, the letter or the CV, will be read first, you should optimize both.
Recruiter here, and this is exactly right. Three good sentences in a 'cover letter' and you won't even make me need to read the resume at all. You should be able to do it in under five minutes.
First, if you are exclusively (or primarily) applying through online applications I'd strong suggest you reconsider your search strategy. That strategy is not nearly as effective as getting in through a side door - the front door is crowded, and the bottleneck tends to get most candidates ignored. These online applications, with some exceptions, are usually the resumes that get only a few seconds to make an impact - you might lose your reader in the first few sentences (note: I haven't worked in big company recruiting from an internal role, but this is pretty widely acknowledged and studies have been released confirming how little time is given to a resume in these conditions).
Why do some companies not accept cover letters? For one, nobody wants to read them. Keep in mind, nobody wants to read cover letters OR resumes. They want to have a conversation, and they want to be able to determine as quickly and accurately as possible whether or not that conversation is worth having. This can be quite prone to bias.
Most cover letters simply reiterate what the resume says, but in a condensed format, along with some fluff about how hard they work and how strong their soft skills are. It's usually fairly pointless, and some companies ask for them as a bit of a test of your interest. Companies that don't ask for them likely don't feel they are useful, and would rather have their recruiters looking at resumes (and hopefully actually having conversations) than reading traditional formatted letters.
Investor interest and hiring manager interest has this in common: inbound to the candidate is far better than shaking bushes. Even YC alum mentioned how outbound is basically desperate and futile. Not that it can't be done, it's that the probability is much lower.
Cover letter is the TL;DR as how the resume applies to the req with 2-3 top selling points. The resume is like a marketing specifications sheet to sell a phone chat. Etc.
They don't even give me a place to put a cover letter. Last week I spent a half-hour writing a cover letter, and then went through the application and there was no place to put it.
Since most online systems require a doc or pdf format, I've started combining my cover letter and resume into a single pdf. If there's room for both in an application then I'll submit two individual pdfs, but if there's only room for one attachment then I submit the concatenated pdf.
Put a small 'summary' at the top of the resume. I do recruiting 'part-time' for work. Mainly non-computer positions but still in a very specific field. Summaries like this really help. Especially if I'm trying to look through 100+ resumes in an hour or two.
