CDAs as also provide significant fuel saving - a
trial at EMA a few years back saved about 73 per approach on MD11ss and about 30kg on B757s. But they were designed for the noise saving advantages, and do work for that.
Flown properly it should ideally be at constant descent rate until levelling to intercept the glidepath. Of course, that assumes that local geography and airspace allow this, which it seldom does.
Easing off the descent rate on the way down is missing the point completely - the rate should be as constant as permitted all the way from cruise altitude to levelling to intercept the glideslope.
And as others have said - fly the clearance or challenge it!
G