Acts as an Edge Jointer - Run the board through the cut with the sled, putting a flat edge on one side. From that you can square the board using standard cuts.
Cuts a straight edge for any purpose - For example, if you've built a small panel or drawer face that doesn't come out quite square, draw a line that would make it square then use this sled to cut that line.
Mills down rough cut lumber - if you've got a planed board but the edges are rough, or even still a 'live' edge, using this sled you can safely put a flat edge on one or both sides to prepare it for further cutting.
Repeatable tapering made simple - set the fence up and clamp down a stop block. Now you've got a tapering sled that will produce identical tapers on multiple boards without any additional marking or set up.