It allows you to optimize your experience by providing:
(-) Accuracy. When you sync, your trainer can see a comprehensive account of your daily activity and build your personal training program accordingly.
(-) Accountability. Syncing helps your trainer give you a pat on the back when you've done a great job, and hold you accountable when you're not as active.
(-) Convenience. It gives your fitness activities a central hub. You'll be able to get workouts, message your trainer, and track your activity all in one place.
(-) Motivation. There's nothing like seeing your numbers to keep you motivated! If your activity is looking a little low, this is great motivation to get moving.