I had the good fortune of finding an instructor who liked to fail the engine after the downwind checks were completed. In the C-172 with 40 flaps available, it was pretty simple to keep the approach tight and select 40 flaps when the runway appeared almost straight down. With 40 flaps, you need a steep descent to keep the speed up and have enough energy to flare -- especially with an upslope on the runway.
So if you are carrying power on the approach, if the engine becomes unhappy, you might not make it to the runway. Removing flap can cost you considerable altitude.
In cold weather, I do carry a bit of power so that the engine will not cool too rapidly; also a warmer engine will be useful if a go-around has to be done.