At our last refresher course we had confusion about this point, as pilots recently trained in Toulouse by Airbus instructors were told to select Flaps 3 on MCDU, whilst our SOPs clearly still instruct not to do so.
As previously stated, reason is that increment due to failure is to be added to Vls Conf Full and not Conf 3. Once the new speed is inserted (i.e. overwritten) as the new Vapp, then what difference does it make which Flap setting is selected on MCDU?
Somebody referred to G/S mini being available if Flap 3 is selected. I've heard this before. Isn't G/S mini always available when in managed mode, irrelevent if you have selected a speed in the MCDU (not FCU),or not?