Why do police carry a night stick?

A police baton is an effective nonlethal weapon that many police agencies around the world use. Its usually used in riot stations and crowd control. The term "Night Stick " came from 1950's, because police officers used to carry a different kind of stick at the day time. However, many police officers stopped carrying it, and replaced it with the a new one called the "Expandable Baton" which is easy to carry on their duty belts. And its also comes in different sizes 16",21" and 28". On the other hand, the night stick is 24" and its made of wood, while the expandable baton is made of steel.