Why template classes?

Question

I understand why we use templates for functions, but what is the point of class templates? Can someone give me an example?

Answer 1

It just gives you the power to create very abstract classes without type dependency.

Let's imagine you want to implement a class for big numbers in C++. It's obivous that this class should be if variable type. You could then create subclasses BigInt, BigDouble and so on all being based on one template base class.