One theory which is subscribed to by several companies (including my own) is that once the aircraft is in motion the handling pilot (PF) should not be distracted by having to take his eyes off whatever he's doing and that the PNF is quite capable of checking that an action has been carried out.
There is, of course, a danger that the PNF will simply "sing out" the expected response, and that both pilots should be checking and cross-checking each other.
The use of challenge and response is, IMO, a valid one, and I disagree with my company's method of operation. However, they pay me, so until they change the SOP I shall do what they ask of me.