Family Setup

The Apple Watch SE will also be the most inexpensive model to support Apple’s new Family Setup feature, which allows you to setup additional watches from your iPhone for use by kids or other family members who don’t have their own iPhones.

The fact that the Apple Watch Series 3 won’t include Family Setup is likely simply a result of Apple only selling it in the GPS version; since Apple has decided that letting kids and family members keep in touch is an important part of Family Setup — which makes sense since users won’t have a paired iPhone to stay connected — it requires a cellular Apple Watch to operate.