It was a staple with most of the Halo games. It allowed you to create your own levels. You could take an existing PvP level and add or remove guns, spawn points, vehicles, etc., or use a few template levels to create totally new stuff with skinned building blocks, buildings, and natural features like rocks and trees. Halo 4 had the best toolkit, while Halo Reach had the best template levels. I was hoping that Destiny would follow that trend, but alas, nope.