What the title says. Maybe you want your military to take a longer route to the gather point because of enemy buildings shooting them down or giving information about your military. Sometimes AI with access to bombard towers makes 5000 of them all along the path making it extremely time consuming to bring them down without bombard cannons.
With gather waypoints, you can set waypoints to your final gather point; allowing you to dictate what route your military will take.
I know you can simply have the gather point somewhere close to your base and then command them using waypoints. But this would be a nice QOL addition to the game.