How are these two things connected or are they completely independent of each other?
The profile and registration are two independent things. Users can of course store data in their profile in your app, even if they are not registered. For example, they can add their name, e-mail or phone number to their profile. Of course, this is only possible if you have assigned these form fields in the dashboard under Settings > Profiles. As soon as you have activated the registration for your app (via e-mail or Facebook), only the e-mail address from your user’s profile will be used to register for your app. The difference to the profile is that your users can take their data with them and use it on another device.