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

Take performance claims "with a grain of salt".

I've heard a high-rated MIT professor make a claim like that for his favorite thing, and the only reason nobody asked him "why" was because he was a high-rated MIT professor.

Such constructors and destructors might have other advantages, but claims about performance (outside of big-O) are seldom even meaningful except in highly contrived circumstances.