I guess if you reckon its warm enough outside you could get by without it most of the time, but i'd rather have the assurance that comes with the heat on than risk having carby icing at low altitude in one of the most critical stages of flight. Its not as if it is much effort to put the heat on, and you'd certainly regret it if you did get icing. I was told to turn it off at 300'AGL, but you can't go too far wrong following the POH, so i would do what it says.
