The owner of a Collection will have almost all permissions on that Collection’s settings and contents. A few special settings (which are marked with
[Admin] in the UI) are reserved to Site Admins though.
Additionally, the Owner will be used mostly every time a default value is needed: default copyright message, recipient of the default contact form, widget that displays the photo of the owner…
Finally, the Owner can be used to group collection together in navigation menus by using the Same Owner’s Collections List Widget.