Books lack the immediate searchability of online, and cannot be easily scaled and manipulated for view as online can, but they retain some advantages

- you can hold a book open at a number of different locations, and easily move between them for cross-referencing
- I find I can also mentally "visualise" the structure of a physical book and its content more readily than online
- a large format book can generally present more information than the average computer screen
- books are portable and don't care what posture or location you are in when reading

Both printed and online have their place for different types of content. Personally, I like printed manuals for complex information, but also like a wiki for quick reference.