Cellular

The GPS only Apple Watch can do  Everything  the cellular model can do  as long as  your iPhone is  nearby, where nearby is somewhere in the same 3-4 bedroom home (assuming typical wood frame construction).  And of course when the iPhone is with you when you leave the house.

https://support.apple.com/en-us/HT205547

The Cellular Apple Watch allows you to leave your iPhone at home while you go for a walk, run, bike ride, etc...

The Cellular Apple Watch shares the iPhone's phone number.  This requires the iPhone cellular carrier to support the Apple Watch.  The iPhone carrier charges a monthly fee for this service.  In the U.S. the fee is $10 per month added to your iPhone bill.

iPhone Cellular Carriers that support the Apple Watch, which models, the radio frequencies each model uses, and the country where they offer service:

https://www.apple.com/watch/cellular

The difference is that it has cellular.

The cellular option lets you have internet access when the watch is away from wifi and your iPhone so you can continue to make and receive calls, and send and receive messages. You need to add the cellular watch to your iPhone's service plan, and it takes on your iPhone's number.. So any calls to the iPhone are received by the watch too.