The documentation about page-level filters talks about the "Allow segments" option:
But what are "segments", in this context?
Segments are a beta feature right now which allow you to define groups in your dataset based upon certain criteria.
"Segments allow you to quickly perform market share analysis and measure one group of data against another. With Segments, you can examine different subsections of your data while still having a constant reference point in your visualization.
In Analyzer, Card creators can define which filters impact each Segment and which do not. When implemented in this way, you can use filters to view other parts of your business while your Segment stays constant."
That checkbox is allowing users to filter based on defined segments as well as other data fields in the dataset.