The complete mystery re: which elements of an application and interview are must-have or must-ace and which are ignored entirely, downplayed, or even taken as "red flags" ("what might that be?" wearing a suit to an interview, or just dressing above business-casual—required some places, practically a guaranteed "no" others) is one of the most frustrating things about interviews. Which is saying something, really, because most things about interviews are pretty frustrating.

I'd recommend presenting yourself and dressing as you'd like. You'll attract companies that are a better fit than one where you're fumbling for the "right" way of doing things.

I trash every application that doesn’t include one. Because most likely they’re just spamming openings, and didn’t read anything about the position.

Every applicant that included a cover letter was way above median quality, and worth interviewing.

I might miss some decent people this way, but it’s been a very helpful first-level filter of applicants.

I suspect most of us have had semi-competent recruitment agents doing the first stage filter for us.

When I look at a CV ahead of a 2nd or 3rd stage interview I take it for granted that they are serious about the role and qualified for it.

I've only paid attention to cover letters for junior positions, mainly to evaluate communication skills.

Do you not consider communication skills important for senior positions?

Some of the worst companies I ever worked at didn't value communication skills for senior positions, and I couldn't leave those roles fast enough!

I haven't hired for senior positions, but I would say that communication skills matter most at the top and bottom, less so in the middle.

A cover letter is an introduction. It's easy, and polite. Skipping it communicates low effort and poor communication skills. I don't want to work with low effort, poor communicators, even if they're genius programmers.

To me they just seem copy-and-pasted and therefore of very low value, almost noise. I want to know if you can get the job done, and that is what a resume and interviews are for.