The original purpose of the engine thermostat dates back to 1930's was to allow rapid preheating of the engine, prior to passing the hot fluid through the heater core (then back to the radiator) for warming the car interior during winter time conditions and allow engines to reach optimum conditions. However, most vehicles can run perfectly fine after removal of thermostats. How many thousands of cracked engine heads have occured because the thermostat got stuck and failed to open has never been counted.
I always removed my thermostats on my vehicles, particularly after I experienced a cracked engine head in college due to a stuck thermostat. I did not have the money for a repair, and so i drove for 6 months with oil in my radiator. Every two weeks I drained the oil from my radiator, until i finally replaced the engine head.
Today's automotive thermostats are extremely reliable and not so much a concern as they used to be, but tractors can operate just fine without any thermostat.