This is another common question I get. Let me try to answer it again (I need the practice).
For readers:
-Optimizes learning of complex concepts.
-Books are like web pages with links that open inline. This prevents readers from having to manage dozens of browser tabs. This often happens to me, for example, when browsing wikipedia.
-Makes books available on more devices than native apps.
-Features such as word highlighting, starring etc.
For content creators
-books can easily include inline sections from other bookvoid books. The author's job becomes part authoring part curation and it saves him or her from writing suff that has already been written.
It is all based on optimal principles of hierarchical information organisation.
In my view, there are very fundament ontological principles, rooted in mathematics and philosophy, that make this kind of hierarchical linking of concepts optimal to human reasoning.
I see it as solving some of the problems that wikis have by providing the enforcement of hierarchy, the inclusion of different levels of details about subjects in a single text and the ability to maintain a chain of trust on material. Anyone can't edit everything like in wikis. If your own books is not popular, you have to have been curated-in by more popular author to gain visibility. You can't simply insert yourself in a popular page like in wikis.
edit: formatting