I have a pretty wide range (at least at the beginning of the evening) being able to sing both a fairly solid baritone and a decent high or first tenor voice. I often use both ends of the range on the same song. For example, my band does Turtle Blues , the old Big Brother and the Holding Co blues tune. I find it effective to start in the lower register, then go up an octave as the song, and the band, gain momentum. Generally, I find it more difficult to generate power in the lower register when singing with the band. This may be because we just play too frigging loud, or because I need to adjust my PA settings, or maybe it's just the nature of the tonal qualities: tenor seems to ring through more clearly.