I'm the developer of an app called
Gym Log+ which is specifically geared towards weightlifting and bodybuilding. Along with the main iPhone app, there is an Apple Watch companion app as well. The Gym Log+ Apple Watch app will contribute to your Activity rings and save your workouts to Apple Health, so you should see your Move and Exercise rings update when using the app to log your workouts. Personally, for me aside from the Activity rings, I just find it more convenient to be able to see my past workout when doing my current workout so I can match or exceed my last reps/sets (progressive overload) from my wrist at a quick glance rather than messing with my iPhone.