use "finsh" event to write msg on response time

I found the "finish" event in node0.6.15/lib/http.js line 813
```javascript
OutgoingMessage.prototype._finish = function() {
  assert(this.connection);
  if (this instanceof ServerResponse) {
    DTRACE_HTTP_SERVER_RESPONSE(this.connection);
  } else {
    assert(this instanceof ClientRequest);
    DTRACE_HTTP_CLIENT_REQUEST(this, this.connection);
  }
  this.emit('finish');
};
```
Is it better to use it than override the original "res.end" ?