Excellent post from Hand Solo!
Altough he is right Airbus Training recommends to use managed descent all times! Most airlines that follow the AI procedures closely do so. They start descent in DES at the descent marker on the ND, reduce the Speed when the FMGS tells you to (where it has been programmed) and reduce to VGD (green dot speed) when they overfly the decel point.
When you get a short cut you get the warning "MORE DRAG", which is the moment they use speed brakes.
My favorite is open descent, where I have complete control over the descent myself. At around FL 100 I use speed and V/S selected and have full influence on my flight path.
I still use the information given from FMGS as a cross check of course. If I'm 2000 ft above the calculated descent path, I'm there where I want to be economically, since in nowadays ATC environment you tend to make more track miles than less.
hth,
Dani