I believe- along with many modern music teachers- that an understanding of the beat is crucial to playing any style of music. I think you’ll agree there? I think one of the best ways to achieve that understanding comes from practising with a metronome. I mean, whatever you’re playing, you’re aware of the beat, right?

Metronomes are essential to making you aware of the beat in the first place, but having said that, I would NEVER use a metronome for performance purposes! As you said, a metronome is a dead, mechanical device, and a musical performance has to groove…but how can you groove if you’re out of time? These are two different aspects here: the internal count (metronomic 1, 2, 3, 4) and the overall groove (produced by the heart of the musician) and there is definitely a skill in switching between a swung rhythm and a totally straight time.

Surely a metronome gives you a more thorough sense of the beat, which then enables you to play around with it from there?

Please consider the alternate views:
http://adamrafferty.wordpress.com/2008/02/27/dont-use-a-metronome/
http://en.wikipedia.org/wiki/Metronome

But take it from an audience perspective: if it really rocks (and I mean really!), then it’ll make you want to move and shake; and feel something. And that can never be done with a dead metronome.