Good question dp.
When I was first checked out on a PA28 I was taught to use carb heat only while doing down wind checks. I did this during a check out on a C152 and the engine stopped on short final. Fortunately I was able to reach the runway. Since then, I leave CH on until I'm on the ground although, in my forthcoming biennual training flight, I will probably have to remember to change to cold on short final.
I always understood that the Continental engine on the Cessna was much more prone to icing than the Lycoming.