I agree with Shanwicks assesment. We are looking to complete the FMC because we feel that it is part of the aircraft and if it is on the aircraft, it should be in our simulation and working correctly.
It is true that VNAV is not widely used in descent on the Classics - pilots use it as a "second opinion" and we like to watch the altitude deviation scale to give us an idea what the FMC "thinks" of our energy situation. It can provide a valuable "heads-up" in some situations. I used it frequently as a "socially compatible" reminder to my FO´s that he is way below profile. "Oh, the FMC thinks you are 10.000 feet low. Well, we both know it can´t calculate very well..." - Silence - FO dials in V/S -200 .
It is very rare that you get to fly an approach fully on LNAV and VNAV in real life - so you need to ad your local knowledge and guestimates to the descent calculation, something you can´t do well in the FMS. Yes, you can add an "expected" shortcut, but if you don´t pay attention and NOT get the shortcut, the plane will turn anyway - leading to a clearance violation.
The only airports I used to regularly fly VNAV into are ESGG and LHBP. They reliably use RNAV STAR and transitions. Everywhere else its FL CHG and V/S.
Jan