When there is a notification, I can use my apple watch to separate out notifications that I need to immediately respond (e.g. important message/call from work or family) vs ones I can take care of later without taking out my phone. Before having the apple watch, I have to take out my phone every time when there is a notification.

I also use Apple pay with the watch all the time without taking out my phone.

Both of these use cases works with non-cellular version as well. Of course you’ll need your phone nearby or have wifi so you can receive messages, but it doesn’t require you to have a cellular watch or have the cellular plan on the watch.