Seems kind of obvious to me:
IFR - you stick to procedure.
VFR - you fly a traffic pattern - as mentioned before ( in different context though), everyone else will know, what to expect. Or did you get tought to turn from final back the long way straight to base? Or fly circles in the middle of the pattern? - Seems odd to me, but then I usually am on an IFR-plan into some busy airport.
And for the A 320- you asked about it: You have to move the Thrust Levers to TOGA, otherwise you don't trigger the GA mode for the FMS... You can retard them a half second later, but they have to go there...