Best to check your Rule Book for the kind of showing you will be doing. Breed shows often have the thimbles or wrap straps on the shafts, no breeching when put to those light show carts. These light carts are driven 99% in arenas, on groomed surfaces, with the various breeds. Not an outside, field or rough track type driving vehicle.
While the Carriage Driving in Pleasure Showing, using the heavier wood-wheeled carts will require breeching in the Rules they show under.
I do think ADS has changed their Rules for CDE Singles, so they now require breeching even with brakes on the vehicle.
It always comes back to the Rules you will be competing under, so you as the Driver/Competitor, need to know your Rules. You HAVE to go thru the Rule Book, learn all those picky details to prevent doing wrong things in situations and being eliminated or ineligable because you didn’t have your harness, attire or accessories done correctly. Not knowing the Rules is your problem, part of not being prepared to compete.
This is an old thread, not sure if OP still needs this kind of information now.