By providing a floating button at the bottom of the page, we allow users to browse, and access filters at any point in their browsing experience. For example, if they scroll through 30 results and realize their search is futile, they can quickly access Advanced Search and refine their query.
Death to Complexity: How we Simplified Advanced Search
Ali Torbati

Please cross check this part in usability testing as persistent buttons in the footer invite unwanted taps while scrolling the list.

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