The Apple Watch Sport is a good 1st generation product that you'll find useful if you want the best of a smarwatch and a fitness band.
It will allow you to conveniently make calls, receive and reply to text messages, keep up to date with social media notifications and more. It will therefore be a useful addition in helping you to keep on top of your busy life.
When it comes to getting you fit it has an inbuilt accelerometer to track your steps taken and your calories burned while using it's Activity and Workout app to give you guidance on how to keep striving towards your fitness goals. It also motivates you to lead a more active lifestyle by encouraging you to stand more and generally become more active in your day to day life.
However in some aspects, the Watch is really mroe of an iPhone extension since features like making calls and GPS rely on a connection to your phone.