I'll be switching to winters when the temp is constantly below 7 degrees during the day. I'll not go a winter on summers again. They make a huge difference when things start to get snowy/wet/slushy.
I know some say, you can get away with out using winters, and I'd agree, but if i was on snow, which is often on my rural commute from Aberdeenshire in to Dyce/Aberdeen airport, and I had to suddenly brake hard due to someone who was sliding around due to lack of talent, summer tyres, experience etc, then the winters can really make all the difference. Winters work better in cold conditions, and you are saving your summers from when it's warmer. Makes complete sense to me.