Most states have laws requiring brakes on trailers above a certain weight, usually either 3,000 or 3,500 lbs. for those brakes to activate, you need a brake controller. Beyond that, sheer attention to safety requires a conscientious driver to have those brakes. You do NOT want to be driving a rig, have a tree or a kid jump out in front of you, and take 2 miles to stop, thus killing the kid and/or yourself.