This is likely to be the more useful answer here. The biggest benefit comes from listing "author of [book you can buy at bookstore]" on your CV or web site. The marketing power of your name being seen by potential employers (or their employees who point to you as the domain expert of a topic). Not from actual royalties past the royalty advance which, as others have mentioned, would be rare.
Of course, the value of that would depend on if you trade on your name; e.g. if you're a freelance consultant.
Of course, the value of that would depend on if you trade on your name; e.g. if you're a freelance consultant.