I believe Notes is specifically meant for Admin or Moderators eyes only and not regular users. Personally I deleted it because I want to see what my users see as much as possible. Say for instance a user may seem suspicious; the admin can leave a not on the profile page that only the admin can see...

Maybe a user is a suspected spammer/scammer...

Admin can add that in Notes on the profile page

Maybe a video uploaded is causing problems or needs to have a source verified. Admin can add source link in notes to keep track...

Maybe a profile needs a badge but Admin is waiting for verification. They can add that in the profile notes or Admin wants to make someone a moderator or potential featured member. They can add that. It's not needed for the most part but I can see how it can be helpful