You use the Apple Watch for many things the IPhone simply isn't capable of doing and also so you don't have to keep digging your phone out of your pocket (or purse, if your of the lady gender) to see what the message is or who a call is from, only to find you didn't really need to dig your iPhone out of your pocket just for that. The screen is not as "dinky" as you think it is.
The watch reminds you to exercise on a regular basis, keeps track of your movements in exercising and calories as you move. It monitors your health and in several instances has saved the lives of people who wear one by alerting them to a sudden change in heart function before they are aware of it themselves in sufficient time to get to a hospital.
I use mine as a handy remote control for my TV that I can't misplace. . . and I can answer and initiate phone calls through my iPhone on it. It's also useful in buying things at checkout stands or drive throughs that accept NFC payments without pulling out a credit card or cash. . . or even being used as a boarding pass for airlines. I've also used it for a ticket at plays and movie theaters. The last four star hotel I stayed at a couple of weeks ago the hotel room door responded to my Apple Watch and unlocked as I reached for the door knob. Very convenient.
It will also give me turn-by-turn silent instructions by tapping me on the wrist, whether driving, walking, or bicycling to get me to any destination.
Plus, I can have my choice of multiple watch faces with multiple customized complications that would make any watch collector drool.
And mine is the original Apple Watch in Space Black stainless steel, which will also run Watch OS3. Try any of that with your $7.99 kiddie toy.
I did give up wearing a $3500 Stührling Limited Edition Meteorite Dial Tourbilon mechanical in Rose Gold in preference for my Apple Watch.