When you apply for a role with an Employer or choose to join their candidate pool we make a direct connection between your profile and theirs. This means that if you update your profile, they will see it immediately. So as you progress through your career, learn new skills, gain more experience, change location etc etc, update your profile and the employer will always see the latest version.
It may be a simple change like updating your availability, maybe now you can work Saturdays and before you couldn't. With a live profile the Employer knows immediately.
Your cover note that you completed for a role will always remain unchanged as will the answers to any screening questions, but if you change your profile after you apply the application will present the latest profile.