Why would the implicitly generated constructor (et al.) be more efficient than a user-defined (trivial) one?

Question

I read this article from D. Kalev this morning about the new c++11 feature \"defaulted and deleted functions\", and can\'t understand the part about performance, namely:

Answer 1

To be honest, I can't see it either.

Among other things, I can see why one should use

class C { C() = default; };

that seems to me the same as

class C { };

Or, if other constructors are provided, as:

class C { 
    C() {}
    // other constructors.
};

I fail to see the real problem the author is writing about here.