There are many cases in which a player might have to walk below a roof and then above it, or there could be a cave system where players have to walk above a place they'd walked past before on a bridge. A DM can create this kind of situation to a limited degree by having multiple similar-looking pages, or they could cleverly design around it. However, having a player see a place they've already past and the progress they have already made is a real storytelling device that can be used to great effect in games. This isn't to mention the bulkiness of workaround solutions that I've used in the past.
Admittedly, I don't have a perfect implementation of this on my mind. It would be nice if there was a simple elevation tracking on the background layer, and designate-able points where object and tokens on their layer automatically moved to track a specific elevation. That may be a little too much for your design philosophy of simplicity, though.
