"See a need, fill a need."
That's good advice with innovation, providing goods or services to others, and writing, especially with technical writing.
Whenever I've ran into different things or got into conversations with people whether it was about a user interface (UI), an API endpoint, how to maintenance or install a part, or a procedure, if there were no documentation on them and I was able to do so, I would write something to fill that need. Or, if the documentation was poor and if possible, I would try to improve it.
I took this advice of seeing a need and filling a need when I wrote my novel, The Unlikely Messenger. At the time, I found no one out there who wrote something similar, especially with the challenges the main character had to face. The theological answer for my character's condition were either lacking or weren't really acceptable (at least for me). So what I did I do? I slowly over 10 years wrote a novel. Looking back, I don't know whether I should have written the novel. Maybe there was no need to do so. But what's done is done. And, I'm fine by it. In the end, I'll have answer to God about the book.
But what happens when there's no need to fill? Or, what happens if there's someone else already wrote similar? So they seemingly filled that need.
The short answer: Don't write it.
Yes. That's right. Don't write. You're wasting your time and energy. Why be just another voice saying the same thing, especially if you don't need to? You don't see, or you shouldn't see, two or more documents explaining the same thing about such and such. So, use your writing for things that don't exist yet.
Besides, you can always look to find needs to fill. It just may not be in the places you're looking at. So, look elsewhere. But if you can't find those needs yet, then wait. If you need to, do something else while you wait. If you also feel like you need to, freewrite or journal. But if there's really no need to write something, then don't write it. (But, if you feel like you have a unique idea, then by all means write it out.) In the meantime, what can you do is observe what's around you and listen to what others say. When you do that, you'll end up writing something eventually.
As for those who've written something already, if you think you can say it better, do so. Otherwise, step aside and just direct or refer others to that piece of writing or documentation if they're looking for such and such. Writing for ego's sake is empty and shallow. Been there, done that.
But I suppose if we only wrote what's necessary, then that would probably eliminate most content out there. Maybe this blog belongs in that pile. Hmm.