In essence, this is to replicate something found in the desktop app. From the online documentation:

“Retrace your viewing path

You can find PDF pages that you viewed earlier by retracing your viewing path. It’s helpful to understand the difference between previous and next pages and previous and next views.

Previous and next pages refer to two adjacent pages, before and after the currently active page.
Previous and next view refer to your viewing history. For example, if you jump forward and backward in a document, your viewing history retraces those steps, showing you the pages you viewed in the reverse order that you viewed them.”