De facto
Please don't tell me that you are one more of the legion of airbus pilots who will use an ALT CSTR in the waypoint and then use managed descent!
Sigh, sigh, sigh
I wrote this because he implied that the use of VNAV or DES is better, and sigh, sigh, sighed someone. Let's not make a mountain out of a molehill.
But I strongly oppose the don't touch "philosophy". It is a dangerous mentallity.
With V/S you can make an optimized descent to an altitude constraint. In DES, the systems is thought for a generic situation, not a specific one. This generic situation is a descent with some altitude restriction. But sometimes you are given a restriction well ahead of the TOD, which is more a step descent than a constraint during a descent to approach. In such cases an idle descent is not always the ideal solution, and therefore DES is not adecuate. But sometimes it is. It depends...
What I do, everytime I am given a constraint, is:
1st: I look at the estimated altitude passing over the waypoint before touching anything.
a) If it is lower than the constraint given an idle descent is in order, I will program the FMGS and use DES.
b) If it is higher than the constraint given, there is no need for idle descent. I make a simple calculation, using my GS in NM/min and the levels to go, and I choose a tactical TOD for either 1,000, 2,000 or 1,500 fpm. I allow for a 1,000 fpm at the last level. The more the levels, the more the rate. At this tactical TOD I set the target V/S. Approaching the point I can see how I go, If high, I'll delay selecting 1,000 fpm for the last level. If I am low, I can keep like that or do it earlier. If I used DES, I would go idle at some 3,000 to 4,000 fpm. Sometimes people use DES when below profile, they get 1,000 fpm al the way, and then they converge to the VNAV path and the last 1,000 ft are made at idle, high rate, then level off... very untidy!
Managed modes are great, except when selected modes can give a more optimized solution. V/S is a great tool. It also allows you to decide the rate at which you gain or loose speed, when accelerating or decelerating. I hate to see a pilot feel unconfortable because the speed is not being reduced as quick as he would like to (for instance in a base vector closing to the LOC) and then overshoot, when they can just use V/S to increase deceleration.
A pilot has to make the airplane do what he wants it to do. Generic solutions and philosophies might not be useful in specific situations.