There are many car owners and even mechanics who have removed the engine thermostat or replaced it with one that opens at a lower temperature assuming it will improve performance.
In reality, if the engine runs outside the operating range at a cooler temperature, its performance declines. A lot of the engine sensors operate based on the coolant temperature, the fuel system may not go into closed loop operation, oxygens sensor may not work properly. Engine computer may be trying to compensate for the wrong readings and fuel economy will decrease.
If you are thinking of removing the thermostat to correct an overheating problem, then you need help diagnosing your vehicle. Always replace your thermostat with one equivalent to the original specs.