While a block heater is not "required" for starting the motor.........it sure is easier for on it (the motor) to not have oil and engine internals at ambient air temperature. I for one am glad my dealer installs them automatically on every new tractor he sells. Cheap insurance in my book. I only plug mine in when temps stay below 15 or 20* and I am anticipating needing the tractor ready for service. I don't leave it plugged in when not needed. I also treat my fuel with proper winter additive and make sure my coolant is current to -30* or so. More cheap insurance. When the white stuff hits I have used my tractor at -20* plenty of times and am glad she has been ready to roll. I have started it w/o the heater a few times sub20*, it did start OK but definitely labored more than when "warmed". YMMV.