I authored and co-authored some books.
I wrote a book on Akka for Packt that has made maybe 5k. Packt is out of India and they have some different standards around topics and contents, but the experience wasn't much different from O'Reilly overall.
And there was a mini book for O'Reilly that netted a couple k, mostly because of later sponsorship.
Writing a book is a really tough experience. I found it taxing. It's interesting going to meetups and having people come up to me and shake my hand though saying they read my book.
I'm not super super happy with either book tbh. It's just such a crazy process to try to get something you're 100% happy with, and once it goes into print that's it forever more.
I would say the impact on my career has been noticeable maybe? You become an expert on a topic by writing well on it because you're forced to fill in all the gaps as you go, and then people give you the credit because you have a book. It sort of happens together when writing a book - becoming an expert and receiving the trust because you're an expert. Even if you thought you knew the subject before, you might find you didn't as well as you do at the end of writing on the topic.