I think that's the thing a lot of people don't appreciate about various device form factors. Pretty much no one needs them but they're more convenient for certain things. I think this was also true of tablets when they first came out. (And as phones have grown in average size the relative advantages have shrunk.)

I don't personally use an Apple Watch. I have a Garmin Fenix that I don't use much. (I usually just wear a $30 Timex.) But I can see why people might like them.