I've been in this game for over 20 years, and never thought of the tip I got from Daz and that funny looking gay bloke, (Matt Bateman). If there's ice on the ground or snow, we only clean down stairs and charge them accordingly. Custy is happy, we're happy, so it's all good. Before you realize it, you've earned a nice wad, and got a few days off as a result. Bad point is, around 33% of your turnover is missing that time around.
Works well for us. On the mainland continent, we tend to get much colder winters than UK, and dryer air, so any warm or hot on freezing glass just goes solid within a second. So WFP is a non starter in winter. Some of the Gurmuns use WFP for high work on commercial work here, so when it's minus 10 to 15, nobody works.
We can work down to about minus 6 with 50/50 mix of screenwash. No detailing though at those temps.
HTH