Calling spinOnce inside a service callback that publishes a message

edit

I have a roscpp service callback that, upon request, does a few things and then publishes a message on a topic. Here is an oversimplified example:

void someServiceCb(std_srvs::Trigger::Request& req,
                   std_srvs::Trigger::Response& resp) {

  if (something)
  {
    std_msgs::Empty msg;
    pub.publish(msg);
    resp.success = true;
    ros::spinOnce();  // Do I need this? Can it cause problems?
    doSomeOtherStuff();
  }
  else
  {
    resp.success = false;
  }
}

The intent is to get the message out as soon as possible.

1. Do I need that ros::spinOnce() in order to get the message out as quickly as possible?
2. Can calling ros::spinOnce() inside a service callback cause problems?