If you lose your phone, and call the carrier to suspend service on the lost phone, are you still able to use the watch for calls and texts until you get a replacement phone?
Also, the watch will work wherever your iPhone still works. So if you’re traveling and pop into a McDonalds or Starbucks and hook up to a WiFi hotspot, your watch will still do whatever your iPhone can do on that WiFi. But non iMessage text doesn’t work on WiFi for your iPhone, thus won’t on your watch.