Both "Cats drink milk" and "Cat drinks milk" indicate generality, but is there any difference between them? Or when there is preference to one than the other?
"Cats drink milk" is a general statement about what cats do.
"Cat drinks milk" doesn't really make sense, unless your cat is named "Cat" (not unheard of :-), or if you're talking about someone or something else named "Cat".
"A cat drinks milk" could also be a general statement about what cats do -- "What does a cat do? It drinks milk."
On the other hand, "The cat drinks milk" is a specific statement about a particular cat.