You use this tool to select Route Choice Mode in the Course Layout Editor.
When you have selected Route Choice mode, you can:
In Route Choice mode, the display in the course layout editor changes from showing the course leg lines that are printed on the map, to showing course leg lines, which are used only for course leg calculation. A course leg line should be manipulated to follow the optimum route choice of a leg between two controls. A route choice line is directional, i.e. there is a different route choice line for the opposite direction.
For more information, please refer to How to calculate course lengths