If the request needs a response, give it i.e. flap, gear, selection whilst flying manually. If it is a PF selected event, PF should announce it, the PNF should check it and only verbally challenge if they think it is not correct. That satisfies a challenge/response check and keeps the inane check chatter down.
Previous post suggests you can fly with the FMA covered - on the Bus, this is not a good idea as there are things that can be selected on the FCU that will not happen unless they are confirmed on the FMA - i.e. constraints in climb, managed descent (VNAV) in heading etc. It is not a problem, it is how the system communicates a confirmation that a selection has been either activated or conditionally activated.