Only when the application actually asks for one, marks the field as required, or is small enough that a personal note is clearly welcome. When the field is marked optional, a generic letter attached out of habit is worse than sending none, and a specific one is only worth the time if it says something the CV genuinely cannot say on its own.
That is a less satisfying answer than “always” or “never,” and it is the accurate one, because what a cover letter is actually doing depends entirely on what kind of application it lands in.
What “optional” actually means in practice
Most large employers now run applications through a portal, and the cover letter field in that portal is frequently marked optional because the system has to accommodate every applicant, not because the company has a strong opinion either way. Treating “optional” as “expected but unstated” leads people to spend an hour writing something a portal is not designed to route anywhere in particular.
A required field is a different signal entirely. If it is required, someone decided it is worth reading, and skipping it or filling it with a placeholder line is a real cost. The two situations look identical in the form and are not identical in what they are asking of you.
What a recruiter is actually doing with it
A note on where this comes from. I worked as a recruiter, at a staffing company placing blue-collar roles, and I interviewed for administrative positions. That is not high-volume corporate screening, and I am not going to pretend it settles this for every industry. What follows is the order things actually got read in, not a claim about every hiring process everywhere.
The CV gets read first, because it answers the fast question: is this person plausibly the thing the posting describes. The cover letter, when there is one, gets opened after that, mostly by readers who are still deciding, not by readers who have already ruled someone out and are looking for a reason to reconsider. A generic cover letter arriving at that stage adds nothing, because the reader is already looking at the CV for the answer. A specific one can genuinely move a close decision, because it is the only place a candidate gets to say something in their own words instead of in bullet form.
When it actually matters
When something needs context a CV format cannot hold. A career change, a gap, or a reason for relocating are all things the CV itself can usually explain in one plain line, but a cover letter is the other legitimate place for that explanation, and for some readers it lands better there than as a note wedged into the experience section.
When the letter is addressed to the actual role and company, specifically. Naming the team, the product, or the exact problem the posting describes signals that the time was spent on this application and not copied across twenty of them. That signal is the entire value of writing one.
When the posting says it is required. At that point the question of whether it matters is already answered, and the only remaining question is whether it is any good.
When it changes nothing
A cover letter that restates the CV in paragraph form gives the reader nothing they did not already have, in a slower format. A cover letter opened with “I am writing to apply for the position of…” tells the reader within one sentence that this is a template, and templates get skimmed, not read. Writing one because a guide said to, without a specific reason for this application, spends time on the part of the process least likely to change the outcome.
What not to conclude
Do not conclude that skipping an optional cover letter costs you the job. For most portal-based applications it costs nothing, because it was never going to be the deciding factor either way.
Do not conclude that a required cover letter is a formality you can fill quickly. If it is required, someone reads it, and a placeholder is worse there than a placeholder anywhere else on the application.
Do not write one letter and send it everywhere. The only value a cover letter adds is specificity, and a letter that could be sent to any employer has already given that value up.
The short version
Check whether the field is required or optional before deciding whether to write one at all. If it is optional and you have nothing specific to say, skip it and put the time into the CV instead. If it is required, or you genuinely have something to say that the CV format cannot hold, write a short one that is actually about this posting and this company, not a paragraph version of the bullets above it.
We do not build cover letters. We build a tool that reshapes the CV itself to match a specific posting, which is the document that gets read first regardless of what else you send with it.