alexban - perhaps you need to practice more Flap 40's?
I assume you do not operate often to slippery or short runways, or in vis of less than 300m? Have you been shown 200m at 50' in the sim with Flap 30 and Flap 40? I can assue you there IS more to see at 40.
The reason (again) is to improve your chances of actually SEEING the required reference in 300m or less, and thereby improve your chances of landing. It has nothing to do with handling, since the aircraft (which is doing the handling, so it doesn't matter whether it is 'practised' at it or not) is equally happy at 30 or 40. The only thing YOU have to do 'differently' is to remember to select one more notch of flap.