Flamenco has a complex rhythmical structure which the dancer is free to exploit but which both dancer and guitarist understand down to the last split second. It follows that a dancer who does not keep in time is going to leave the guitarist out on a limb.
The quote was included in a point about speed - a different matter. It is true that the guitarist will speed up if the dancer does and even (more difficult) slow down. But even here the dancer will have given the command so that the guitarist is accompanying the change more than merely following it.
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