Here are my two use cases for the feature:
1) When mowing the lawn I walk close to the house which causes the watch to try to connect to wifi. If I am streaming music this isn't great, I would prefer that the watch stayed on LTE for streaming.
2) Similar to number one if I start a walk/run from my house I want to get to LTE quick. The watch will try to stay on home wifi for quite a distance sometimes which isn't helpful.