What’s the reason for getting a 180 degree thermostat?
 

I mean, other than the obvious, that it sends coolant through at a lower temp. But why is that necessarily a good thing?

Sleeved aluminum engine,cooler is better to a certain extent and overheats tend to warp heads. Couple that with a temperature gauge that starts to move when you are already in trouble, you need all the headroom you can get.

The higher temps help with emissions, but not enough to matter you are getting about 20 degrees cooler over stock
not a alot but it could save your heads.

Hmmm, OK I see... I have a water temp gauge installed, so I can monitor it closely, but perhaps the best practice is to throw in a 180 until smog time and then put the 190 back in? Was the OEM 180 thermostat made for Disco 2's or is it an adaptation?

You will pass smog with a 180 in. It's the thermostat for the diesel originally if I remember correctly.

What he said. ^

Imprecise.
Directs coolant flow towards radiator at 180F and above.

The original design was that the coolant ran at temps above the boiling point of water for the sake of a tiny bit of emissions improvement. Coolant temps in the 215 to 225 degree F range were considered "normal."

Clearly this scheme only works in a perfectly maintained cooling system. As these vehicles age, just one component of the system failing at those temps could lead to catastrophic failure, overheating.

The 180 thermostat mod is building in a buffer against that failure.

They also just run better when running cooler. Better idle, better gas mileage, better horsepower, better truck longevity, better everything. This is what my rover master tech claimed and I have no reason to doubt him.

This is correct, emmisions is not to make an engine run better. It's to protect the environment. There is a balance. I believe having to rebuild an engine every 60k miles because of over heating is bad for the environment too.

Which is just a farce in the long run anyway.