Welcome Visitor! Please take a few seconds and Yes, that is true in moderate weather conditions.
A t-stat controls/sets the low operating temp of an engine, so a working t-stat can never cause over heating.
Cooling systems are designed for high outside temperature operation, 100+deg, so unless the design is bad an engine shouldn't over heat driving across Death Valley in the Summer, may run warmer but not over heat, that's with a 160, 180 or 192 t-stat.
The t-stat is there to prevent under temp engine operation.
If the outside temp is 0deg, the cooling system can lower the engine temp significantly, the t-stat is there to prevent this "over cooling".
At 0deg engine with a 180 t-stat would run just above 180deg, with a 192 t-stat just above 192deg.
Since engines are designed based on a specific operating temp range, 200-220deg, all the components are setup for that range, including the oil system and combustion mix.
All engine oil viscosity is measured at 212deg, so 30w is 30w at 212deg, at 180 it might be 40w, not a big deal but not nothing either.
Running an engine below optimum temperature, on purpose, just doesn't make sense, lubrication and mileage are both negatively effected, granted as you said not much.
But there is no benefit to run at a lower operating temp, so only a downside no upside.
If you are after a horsepower increase then running at a lower temp will help, the intake is heated by the engine, lower engine temp = lower intake temp.
Rule of thumb is 5 deg cooler intake temp/air mix = 1% more horsepower
The lower temp does come with what was said earlier, lower mileage and lubrication, but if you are after horsepower then mileage is not a concern, lol.
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