By sharing a status update to your profile, you are able to share how your workouts are going with your friends, you are able to keep people up to date with your training and if you are trying any new workout routines, ability to update new body stats and workout routines that you have shared to the database.
Keeping yourself and your friends up to date with your progress helps keep you motivated and focused on your fitness goals as you can see and view the changes that you have been making with your workouts.
Your friends are able to comment on your status update to send you support, feedback and motivational words to keep you pushing forward with your training.
Status updates and posting on your news feed is important by keeping your friends up with your progress and being able to receive the support and feedback with your friends. By also posting these updates for yourself, you are able to keep up your drive and focus for what you are trying to accomplish.