Engines have a preferred operating temperature and the goal is to keep the engine at that temp at all times, under all conditions. Running the engine hotter or cooler than the preferred temp hould be minimized and/or avoided if possible.
In a perfect world, what we'd really like is an engine
heater to warm the engine and oil to operating temp prior to even starting the car! Then we'd like a thermostat to maintain that optimal operating temp throughout all ranges of use and external temperature extremes. This could be accomplished by having infinite cooling capacity at all external temp extremes.
Problem solved!
Running the car without a t-stat will delay getting the engine up to operating temp. On cool days, the engine might not ever get to operating temp because the cooling system (radiators) are always in the loop.
Thus, the low temp t-stat is an easy and cheap way to get the engine up to the preferred operating temp and keeping it there without modifying the cooling system and spending $$$ to do so.
To carry this discussion on to the next logical step; the next move towards that perfect system would be to increase cooling capacity by installing the Boxster S model center radiator into the base cars or install more efficient raditors.
Our Forum owner has provided a convenient DIY that shows how to install the Boxster S center radiator. The parts kit new is $1,100 but you can often find a used S radiator and piece together the hoses and other parts for much less:
Boxster Center Radiator Installation.
More efficient radiators for the Boxster base cars can be found here (among other places):
Porsche Aluminum Radiators