[Larry]

A brake controller is only used for larger trailers that have electric brakes on them. Electric brakes work by energizing a magnet which grips against the brake drum which in turn applies the brakes. The controller adjusts the amount of electric going the to magnet thus determining how hard the brakes are applied. Small trailers for snowmobiles, small boats, personal watercraft, and lawnmowers usually do not have brakes on them. Many States require brakes on trailers if the trailer and load exceed 3,000 pounds. The last thing you would want is to have a heavy trailer pushing you down the road!
I tow a gooseneck flatbed with my Tundra. The trailer is 4,400 pounds empty. You can easily tell if the trailer brakes are working or not!

What I don't understand about Toyota's thinking, is why would they have a tow hitch, towing package with all electrical wiring, but NO place to install the brake controller? I removed the ashtray and used double sided tape to mount the controller in the bottom of the hole. I then unscrewed the trim plate from the ashtrap and taped it back in the hole where it came from. Now it sort of looks factory installed.