I’ve noticed a few differences.
The arc of the sun will change according to the latitude of the region representing, to a degree, what happens in nature.
The closer you are to the equator, the higher the Trainz sun will be at midday.
It’s also interesting to see the sun correctly arcing towards the north when choosing Australia. It always seem odd to me as a resident of the northern hemisphere that the Oz sun appears to be moving backwards!
You can also change effect in any region if you alter the World Origin lat/long co-ordinates.
The choice of region also makes quite a subtle difference to the way the terrain and objects are lit. I make both UK and Italian routes and choose Switzerland region for the latter. That choice gives me RH drive for the vehicles and is the closest choice in lat/long to the Mediterranean. I then fine tune it further by changing the Word Origin co-ordinates to the correct location, further south. It definitely improves the lighting which can be seen changing across the baseboards when the co-ordinates are altered.
The second difference, in older versions (I don’t know about TS12), is that the Objects flyout automatically defaults the Object region panel to the one selected for the route. This reduces the choice to only those objects which have been tagged with that region. Not terribly smart because lots of assets have been incorrectly tagged. Fortunately it can be overridden by choosing “All”.
I can’t say I can immediately recall any others, but I’d be interested in other members’ experiences.
Cheers
Casper