Gandalf's riding

I'm just curious. In fact I like the movie very much and I have never rebeled against PJ's work. If somebody comes to me and tell something like "PJ did so many mistakes. How dares he cut Tom Bombadil's scene off..." etc.., I think "If you are so smart and competent - why don't you try to make better work." And I still stand on this position. <BR>But I have one question though. Just b/c I'm curious about it. <BR>The scene when defenders of Osgiliath ride to Minas Tirith trying to escape from nazgul's attack. At that moment we can hear voices from the Minas Tirith "Mitrandir! The white rider!". And we see Gandalf's riding to rescue defenders. But why he took Pippin to this riding? Hobbit must be like an encumbrance at that moment.<BR>I just can't realize all genius of such director's position. What do you think about meaning of it?