W in CWS actually refers to control wheel, more widely known as yoke and not that small pitch thumb wheel on AP control panel. ATR´s TCS worked a bit differently compared to Boeing CWS. When you pressed and held it, it would disconnect AP servos, leaving you in manual control of the aircraft. When released, vertical AP mode (pitch, VS or IAS) would reset to current value.
Except for practice, I cant recall using it in my 2500 hrs on ATR. Also where I fly, level flight on MDA is a big no-no. We´re fans of continuous descents and VDPs.