It's really simple logic. If both vehicles have brakes, the emergency stopping distance will be shorter if only one has brakes.
Under normal driving conditions, supplemental brakes are redundant; however, under emergency conditions, every little bit helps.
And as mentioned, breakaway brakes are required in most (if not all) states. So, if you happen to get into an accident, you can probably bet the either the LEO or your insurance carrier will bring this up with the possibility of a large fine (citation) and/or loos of insurance coverage.
Expensive? Yes, but compared to what the consequences can be...it's really cheap.
Ron
Ron & Sandie
2013 Tiffin Phaeton 42LH Cummins ISL 400hp
Toad: 2011 GMC Terrain SLT2
Tow Bar: Sterling AT
Toad Brakes: Unified by U.S. Gear
TPMS: Pressure Pro
Member of: GS, FMCA, Allegro
RETIRED!! How sweet it is....