I'd also point out that just as a musician needs to develop good time, so should a dancer.

We can't have all you peg legs gallumphing around off the beat and then blaming it on us down here in the pits when it goes wrong ...

a dance leader counts out time and cues at rehearsals - acting as a kind of .. hmmm ... now what can I compare them to ...

... maybe ... something like ... a metronome ...

       ^_^