Mainly cold engine protection. You need a really thin oil in subzero conditions, so it can flow when cold. you need a heavier oil when hot .

The road to Valparaiso was fantastic: great pavement, winding twists and turns and, most importantly, reasonable speed limits. One of the things we appreciated the most about riding in Chile was the fact that their speed limits were realistic maximum safe speeds for each type of road. We never sped in Chile; it actually felt unsafe to go much faster than the speed limit. They even had provisions for bad weather and heavy traffic. Coming from Canada where, at the slightest complaint from an individual, road speeds are changed arbitrarily and without any consideration to the type of road it may be, it was refreshing to see that the Chileans had put some thought behind their traffic laws. Their chevron system was pure genius. Three successive chevrons are painted at intervals in each lane. If you can see all three chevrons (i.e. traffic is light and/or visibility is good), you can go the posted speed limit. If only two chevrons are visible, it is assumed that traffic has become dense or the weather/darkness has reduced the visibility, and therefore you are required to drive slower; and if only one is visible at a time, slower still. I wondered why Canadians didn't implement the same type of system.
The Great Pan American Motorcycle Expedition  Jesse & Jessica Eyer pp244-5