What is the extra band on the bridle for?

it keeps the horses mouth closed, its called a flash strap its mostly for horses that open there mouths while riding or chew on the bit a lot, you don't need it on there unless you want it but you can take it off and not use it most people do that. if you are going to put it on put it just under the horses mouth but dont tighten it to much or its bad for there breathing you should be able to get 1-2 fingers under there with out it being tight