Sorry for the thread drift, but I wonder if Appleseed and Dorothy can both be serious about a drummer as mere 'metronome'? And ditto to the Zappa reference suggested of course, among numerous others.

As a generally unaccompanied singer I've found that some percussion can be great (both to listen to and to receive) but in both instances I've been aware of the drummer observing the singer for cues as to how the tempo should be going.

The only time I saw this go wrong (though to no serious effect) was where the unexpected accompaniment (to a usually unaccompanied singer) happened to be blind, and as as such he wasn't able to follow any subtle cues as to where she wanted to shift tempo wise.

Otherwise, I do believe the drummer is more than a mere metronome. And that well crafted shifts in rhythm and tempo are one of the numerous pleasures of engaging with music.