Operator Overloading helps users/developers use a particular
class in an intuitive manner for different kind of
operations logically possible on the class. 
It's used for ease of code read and maintainability.

e.g. Date 'b' can be subtracted from another instance of
Date, say 'a', to get the difference in number of days
between the two days.
So, you would overload the subtraction operator '-' for the
Date class accordingly.
Date a("07/04/2008);
Date b("05/04/2008);

//operator overoading for '-' for Date
//returns number of days
int Date::operator-(const Date& rhsDate)
{
   //wotever logic
   return <number of days between the (this) date and rhsDate>
}