Just to be clear. The GPS only Apple Watch can do Everything the cellular model can do as long as your iPhone is nearby, where nearby is within 40-50 feet of your Apple Watch, such as a typical 3-4 bedroom home.
The cellular can still make and receive phone calls if you leave your iPhone at home while going for a walk, run, bike ride, etc...
I am the kind of person that keeps their iPhone with me at all times, so a GPS only model works well for me, I've held extended phone call conversations on my Apple Watch and the person on the other end never knew I was talking through my watch.
Others in the forum, like to leave their iPhone at home when walking, running, riding, etc...
While the cellular model does cost more than the GPS only model, you are not required to add the Apple Watch to your iPhone contract, so if you decide you do not really need the cellular after purchase, or you want to save the monthly extra charge, you can use a cellular model as if it was a GPS only, by stopping the cellular service with your carrier.