The reverse filter is used to reverse tracks and routes. It's mostly useful for those few formats where track/route sequence matters and there isn't a way to reverse them using the program itself.
The reversal is performed in the laziest way possible. Timestamps are kept with the original waypoints so the resulting track or route will have the interesting characteristic that time runs backwards. This tends to make Magellan Mapsend, in particular, do a wierd thing and place each waypoint on a separate day.
Additionally, if you're using this to reverse a route that navigates, say, an exit ramp or a one way street, you will be in for unpleasant ride. application cares about timestamps