Why using reference as a parameter is inefficient with built-in types like int or double?

Question

I have encountered this sentence in the following blog entry ( https://latedev.wordpress.com/2011/11/16/c-stringstreams/ )

Secondly, the use of a reference as a parameter is a little inefficient for the built-in types like int and double (...)

Is this true? If so why? I've always thought that it's better to use references not to produce copies for methods like :

template <typename T>
string ToStr( const T & t ) {
  ostringstream os;
  os << t;
  return os.str();
}