Do I really need a thermostat?
Beleive it or not, thermostats help a great deal when the car is in traffic. When you're just circulating coolant with no restriction, it passes relatively quickly through the engine, picking up a moderate amount of heat. It then goes to the radiator, where that moderately heated water moderately cools. The actual amount of energy transferred is fairly low.
Now with a thermostat, all the water exiting the engine is at least the rating of the thermostat, say 180 degrees. The hotter the coolant when it enters the radiator, the more total energy leaves the coolant while in the radiator (the bigger the temperature difference, the faster the flow of heat) so to a point, you want the coolant as hot as it can be (within reason and within the performance limits of the engine) as possible for the maximum heat transfer through the radiator.
In stop and go traffic, where there is only the air your fan is pulling going through the radiator, you need the most efficiency you can get, and that means hotter coolant temps in the radiator, which equals a hotter thermostat.
Without a thermostat, you can have issues with the car warming up (it could possibly never come up to operating temp) Or without a thermostat, the engine coolant temperature could misrepresent the actual engine temperature, because the coolant has not spent any time becoming acclimated to the engine temp. You could be overheating your engine and causing hot spots in cylinder heads and walls without your temperature gauge ever indicating so.
Now running without a thermostat is possible, and isn't guaranteed to mess anything up, if you let your engine come up to temperature, and pay close attention to it. But on a street car, you should definitely use a thermostat.