In what cases have you applied the concept of abstract classes in your practice?

I have applied abstract classes in Java when I need to define a common behavior template for a group of related classes, but the base class itself should not be instantiated. For example, when there is a base class with partially implemented methods and abstract methods that must be implemented in subclasses.

Example: I had an abstract class Animal with an abstract method makeSound(). Concrete classes Dog and Cat implemented this method differently. This allowed me to use polymorphism and ensure that all animals have a method to make a sound, but the implementation depends on the specific animal.