I'll tell you what they are good for, and that's reference!
I'm not an experienced DB coder by any stretch of the imagination, but just browsing through the books helps to you know which commands do what.
For ages I was trying to figure out how to apply a tint to a sprite, so I could use a base white sprite, and then apply different colours at runtime. Five minutes looking through the book and I found the answer ("set sprite diffuse" if you're interested)
The DBP help files are useful, but unless you really know what you're looking for, it can be a bit like poking around in the dark. The books help shine the light.