I often shift to a lower cadence when drafting particularly if it's at all down hill (for me that's around 70-80 instead of 90+ when leading). The bike accelerates slower in response to a given pedal force the higher the gear, so IMO it's easier to main constant speed and minimize rubberbanding. Also, high cadence may be best for optimum power output, but at low power the effort needed just to maintain a high cadence can be a waste of energy.

Agree that if you're not putting any tension on the chain then you're coasting whether or not your legs are going around.