delegates

Call a method using Class object:
Calculator c=new Calculater(); // c is a object of Calculator class
c.Add(10,20) // Add is a method it takes 10 & 20 and returns int type [30]

Call a method using Delegate:
delegate int PerformCalculation(int x,int y); //delegate declaration
PerformCalculation p=new PerformCalculation(Add); // map delegate with method
p(10,20); //call method

My doubt is:  so many authors said that delegates call a method at runtime...This is an advantage.....
  Normal Class object call the method at runtime..Is it correct or not ? .....
any one knows... pls ...explain this correctly[At compile time and runtime mechanisms what will happen in both scenarios]
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