Quick A: Because they reduce code duplication, and so make code more readable and maintainable.

Recently on SO:

Why did C++11 introduce delegating constructors?

I cannot understand what the use is of delegating constructors. Simply, what cannot be achieve without having delegating constructors?

It can do something simple like this

class M
{
 int x, y;
 char *p;
public:
 M(int v) : x(v), y(0), p(new char [MAX]) {}
 M(): M(0) {cout<<"delegating ctor"<<endl;}
};

But I don't see it, is it worth introducing a new feature for such a simple thing? May be I couldn't recognize the important point. Any idea?