How are Functors useful?

Question

We know that any generic type F[_] withmap method, which complies to some laws, is a functor. For instance, List[_], Option

Answer 1

Well, once you know something is a Functor, you don't just get map, you get all of the functions you can derive with it too

For example, it's possible to derive the function lift in a way that works for any functor.

Lift will "lift" a function from A => B to F[A] => F[B] for some Functor F[_] and is defined as

def lift[A, B](f: A => B): F[A] => F[B] = map(_)(f)

If you are using a library like cats or scalaz then you get these functions for free. The cats documentation has a few other examples you might be interested in