To be able to group Interface Designer's pages into sections. Additionally, to access them via hover/clicked dropdown or mega menu at the top when the Interface is published.
How does it solve user problems?
If a user has multiple pages in the Interface Designer, the user should be able to group them into different sections for a cleaner, more organized view. Like data table views having sections on the left, pages should, too, as they act as an alternative to table views.