Ok, I guess my general point was meant for those in FAR 91 and other categories that are not obliged to turn on the anti icing "on".
Apparently guys in England (Birmingham, Challenger accident) did not do it. And they are not alone in not doing it.
It is not about flying in "known icing conditions" - it is about leaving you a/c small as a GA or as big as GV, Global or Challenger out on a tarmac overnight.
The icing on the cake can be so smooth you don't feel it.
If the OEM gave you already a hefty blow torch in form of the anti icing (believe me, I've seen burned ribs on Challengers!) you better use it.
Res ipsa loquitur