The footer code i.e. _satellite.pageBottom() is responsible for identifying the end of the page for timing control Hence fired just before DOM ready event. This code snippet should be placed in the body section of the site code as close to the closing tag as possible.
_satellite.pageBottom() is what compiles all the variables defined on that page into an image request and sends it to Analytics servers . If you are familiar with legacy Adobe Analytics implementation , _satellite.pageBottom() serves same purpose as s.t() call.
With what I see, if we choose the option load library on top of the page even if i do not place the _satellite.pageBottom() - beacons still fires just fine. I am skeptical _satellite.pageBottom() does same as s.t()