A true CDA includes minimum thrust too remember, which is very much unachievable in a lot of places today. "Speed up" right after you've commenced your descent throws any proper CDA right out the window from the get go. Then "slow down", out comes the speed brake, and you wonder why we bother.
Anyway ..
Am I low? I go V/S.
Am I high? I go LVL CHG
Under vectors and have some capacity to doodle a realistic LNAV path, or is my PM willing to ... then great, VNAV it is (unless I'm expecting even shorter miles, I'd stay below the VNAV profile a bit)
Is it totally perfect? no. Though, I don't think I have ever levelled off unintentionally with the above approach. There is a book out there with all sorts of formulae that prove it can be an exact science.I personally half can't be assed and half don't want my brain zapped away doing all manner of formula whilst I'm flying and trying to free up capacity.