cellular on apple watch

NO

Also be aware that not all carriers support the Watch.

The advantage is that you don't need to have your phone with you. With a cellular connection, your watch can make and receive calls and messages, stream music, all without your phone. People often like to do this if they're going for a run where the phone would be added weight, or to the gym where it could get stolen if left in a locker.

Only you can decide if the feature has value for you, though.

Glad it helped!