This is for when the chicks bunch together, making it hard to track them. Because the automatized version of the tracking may have some kind of error when the chicks are right next to each other, the user would need to be able to adjust the tracking of the chicks so that it would be correct. Otherwise, you could run into major problems when a couple of chicks standing next to each other form a yellow blob, which could make the program think there is a single chick in that moment or may confuse the positions of the two chicks.