Having personally operated the first commercial PT-6A powered airplane on the US west coast, circa 1966, ice deflector vanes should be used only when absolutely needed.
To do otherwise is poor advice.
As concerning windscreen anti-icing heat...only necessary where the AFM recommends same, and....with NESA heated windshields, especially....referenced, F.27/FH227, DC6, DC7, Lockheed Constellation, Boeing Stratocruiser, CV340/440, (etc) aircraft.
Others?
Consult the applicable AFM for the correct information.
Do not make it up as you go along...problems otherwise.
RTFB.