The 'Traditional Grip' came about because early marching drummers hung the drums on their bodies with a rope. This caused the drum to hang in a very extreme angle to the drummer's left side. This left hand grip helped the drummer strike the drum without assuming an uncomfortable shoulder position. Modern marching harnesses allow the drum to remain level in front of the player which is why some marching bands have since adopted the matched grip. It's all good. The music is what matters most. Use what suits you and is comfortable.