The Canon EW-88B Lens Hood is designed for the Canon TS-E 24mm f/3.5L II Lens. The hood is primarily designed to prevent unwanted stray light from entering the lens by extending and shading the end of the lens.
In addition, since the end of the lens is extended, you also get the added benefit of some extra protection from accidental impact. The lens hood features a twist-lock mount for extra security, to prevent losing the hood.