The Canon ET-60 Lens 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.
 
Compatible Lenses
 
EF 75-300mm f/4-5.6 III
EF 75-300mm f/4-5.6 III USM
EF-S 55-250mm f/4-5.6 IS II