What's the use of the private copy constructor in c++

Why do people define a private copy constructor?

When is making the copy constructor and the assignment operator private a good design?

If there are no members in the class which are pointers or handles to a unique object (like file name), then wat other cases are there where private copy constructor is a good idea?

Same question apply for assignment operator. Given that majority of C++ revolves around copying of objects and passing by reference, are there any good designs which involve private copy constructor?