title: When to use emplace* and when to use push/insert
body: <p>I know of general idea of emplace functions on containers("construct new element inplace").<br>
  My question is not what it does, 
  but more of like Effective C++11 one.</p>
  
  <p>What are good rules for deciding when to use (for eg when it comes to <code>std::vector</code>) 
  <code>emplace_back()</code> and when to use <code>push_back()</code> and in general emplace* vs "old" insert functions?  </p>