 The fight between Yoda and Dooku was envisioned quite differently.  Originally, Yoda was to come in and immediately have the fight with  Dooku, but many of the creative team felt that was too quick a  transition for Yoda, and the audience needed to feel the power of  good and evil going against each other, so George Lucas (qv) added  in the preamble to the fight with the blue lightning and rock falls,  because it showed how powerful Yoda was. The light saber battle was  a culmination of all that energy.