Dipping a toe in some turbulent waters...
Handflying:
Readbacks are only helpful to the controller and therefore enhance safety up until they become a hinderance. At that point, because they eat up his time for issuing subsequent instructions and delaying what he wants to do with the BIg Picture, they become counterproductive to safety.
Am I alone in seeing a problem here? If a controller/frequency is so busy that all the controller can do is issue (hopefully correct) staccato instructions and clearances (which are hopefully heard correctly) machine-gun fashion with no time for the readbacks that would normally be considered essential... well the problem is serious and dropping the requirement for readbacks is NOT the solution!
R1