Book of Knights is essential reading for anyone playing said characters in Pendragon aka King Arthurs Britain. It gives easy access to information and a few tables, enabling a player to concentrate on the story, rather than spend half the knight finding the blunt penknife vs armadillo table that some games systems require. For a tyro to the system, the book also gives some biography examples that would help them to set up a character portrait for entering the story.
Fairly light and durable for a paperback - a definite plus if in regular use.