What is DocBook?
DocBook is a format. It is a document format. It is not the paper or the screen or the words. Instead it is a way to organize the words in a document. DocBook is not the layout and styling of the text. It is a way of labeling the different sections of the content by structure and semantics, sort of like using <h1> and <h2> but on steroids.
What’s good about it?
It makes the presentation of the written words available on every device and every technology. You only have to write it once, and it changes in all of the formats. You can have a printed book along with an eBook along with the exact same information to send to any other device not yet invented.
Why use it?
Technical writers use it for some of the same reasons you use punctuation to differentiate between two concepts when they appear in the same sentence. They also use it for the same reason you put paragraphs and chapters in books. DocBook is a way to group information that a computer can understand so that when other people want to find specific parts of your work they can. And though DocBook is not the way to style the text, it facilitates the universal formatting of different types of sections.
Who Uses DocBook?
The software industry uses it to write about their products and features. It is also used in many other industries and hundreds of companies to construct their user manuals. It is used for enterprise-wide content organization and eBook publishers.
What Would You Not Use it For?
While DocBook is an excellent and widely-accepted way to organize concepts, it might not be the best choice for extremely large data sets which are more task-oriented. If this is your main type of document, or if you have to include a lot of external references, or need it to integrate into on online help system, then maybe DITA is a better choice.