PA28 POH in Section 4 "Approach and landing" clearly states "Carburetor heat should not be applied unless there is an indication of carburetor icing, since the use of carburetor heat casues a reduction in power which may be critical in case of a go-around. Full throttle operation with carburetor heat applied can cause detonation."
To comply with this we apply carby heat on downwind and make sure there is no icing then leave it cold on the approach.