Why is namespace composition so rarely used?

Question

In his book The C++ Programming Language (third edition) Stroustrup teaches to define individual components in their own namespace and import them in a general namespac

Answer 1

I feel the other answers have left out the first, simplest, and most useful way to compose namespaces: to use only what you need.

namespace Needed {                                                                                                                                                                            
  using std::string;                                                                                                                                                                          
  using std::bind;                                                                                                                                                                            
  using std::function;                                                                                                                                                                        
  using std::cout;                                                                                                                                                                            
  using std::endl;                                                                                                                                                                            
  using namespace std::placeholders;                                                                                                                                                          
}                                                                                                                                                                                             


int main(int argc, char* argv[])                                                                                                                                                              
{                                                                                                                                                                                             

  /*  using namespace std;                                                                                                                                                                    
      would avoid all these individual using clauses,                                                                                                                     
      but this way only these are included in the global                                                                                                                                      
      namespace.                                                                                                                                                                          
  */                                                                                                                                                                                          

 using namespace Needed;  // pulls in the composition

 string s("Now I have the namespace(s) I need,");

 string t("But not the ones I don't.");

 cout << s << "\n" << t << endl;                                                                                               

 // ...

Thus any conflicts with other parts of the STL are avoided,as well as the need to preface the common used functions with std::.