I've done a lot of reading about writing. Mostly to procrastinate writing. It's been useful in some ways. I've learned a lot about the publishing business. But I think the craft part--stuff on how to refine your writing and make it better--has been a waste of time.
You either know how to write or you don't. Everyone has a unique style, and some people's writing might have the same consistent weakness. But if you have certain problems in your writing (like waxing poetic instead of using your narrator's voice in my case), then what you really need is for someone else to read your writing and tell you what's lacking so you can fix it. Some author you've never met isn't going to know what you need to work on. They might write about what they need to work on. They might even have some good general advice. But it didn't do much for me.
The problem is that I became way too self-conscious about my writing. I'd want so desperately to avoid the writing pitfalls they mentioned that I'd go the other way. In my first manuscript, for example, I worried that it was too dialogue-heavy. So I cut out lots and lots of scenes. And then people would read it and tell me, "You should make this a scene."
It's good to have an editor. But when you're the editor, and you're your own worst critic, sometimes you can go too far.