The best bands I have played in have had a great drummer. A drummer who is the orchestra leader... the conductor from behind the drums. Of course everyone needs to have the arrangements down, but the drummer is the one leading the charge and driving the band. When the bridge is coming up or the ending, the drummer lets everyone know. A great drummer plays with confidence and knows how to push the beat, play behind the beat and play on the beat. A drummer can have great chops, have all their rudiments down, can play a solid solo, but if the confidence and song structure is not ingrained, the song will never become magical.