Most common case of 'Dual Input' scenarios, IMVHO, is during the training of new convertees to the airbus.
As the aircraft has no sensory feedback from either the side stick or the throttle quadrant the instructor in the LHS must 'gauge', 'judge' or 'anticipate' what the trainee is going to do, especially in the flare.
It is an odd system that provides additive input as one of the most common requirements for assisted input is in the landing flare when you need to be extra careful that you are not feeding potential recovery input into the stick for a badly judged flare at the same time as the trainee 'hoicks' in a handful of stick to arrest the ROD.
You get used to it pretty quickly though.