The only difference between a page and a subpage is that a subpage contains it’s parent in the URL, as will any pages that sit as children to the child page…
For illustration.
Regular page:
example.com/a-page/
Subpage:
example.com/a-page/a-child-page/
Sub Subpage:
example.com/a-page/a-child-page/another-child/
and so on…
Aside from the URL there’s no other differences i can think of.