Whether you need a thermostat or not, is really a matter of what you need to accomplish and the capability of your cooling system. If you need or want your engine to come up to a particular operating temperature as quickly as possible and stay at that fairly precise temp, (provided that you have a properly-sized and efficient heat exchanger (radiator)), you need a thermostat. That’s why all vehicles come with them as standard equipment. If your cooling system is not adequate to function properly with a thermostat (because they are a flow restrictor, even when fully open), or you need to operate at a temperature that is lower than what a typical thermostat is designed for, removing the thermostat might help you achieve your goal. You just lose the ability to control the coolant temperature (unless you’re using fan controls to control temp). If your cooling system is still not able to prevent an overheating condition after removing the thermostat, you need to improve the capacity/efficiency of the cooling system.