1 Timothy 2:1
I exhort therefore, that, first of all, supplications, prayers, intercessions, and giving of thanks, be made for all men;
  For kings, and for all that are in authority; that we may lead a quiet and peaceable life in all godliness and honesty.

Our Prayers are not a waste of time, when we get to heaven we are going to see how much each of our prayers made a difference