Pulling breaker when towing.

All vehicles are set up so that when the brake pedal is depressed, the brake lamps come on. If you have a supplemental brake system, the towing vehicle's turn signals can be overridden by the towed vehicles brake lamps unless the supp brake system takes the override into account and isolates the brake lamp switch/circuit (My US Gear UTB does this). Pulling the brake lamp fuse does the same thing. Some folks put a brake lamp switch isolation switch in instead of pulling the fuse.

Pulling the brake fuse releases the emergency brake and allows it to roll freely

In my Saturn pulling the fuse isolates most of the systems that would draw down the car battery. Before I installed an extension to a remote fuse under the dash I would occasional be lazy and not pull the fuse for short trips. True, there was no problem as the battery could easily handle the one or two hour draw. However, once, either because the battery was weak or I left the radio on or whatever, I stopped to find the car battery "dead". After that experience I made the fuse extension and ran it to the dash. I see in the RV magazines that you can now purchase a similar product with a switch. I just shorted out a 30amp fuse, soldered an appropriate wire to the test points on the fuse, put the wires through the firewall of the car, and placed a new 30amp fuse in line. Jerry Built but it works for me.
Happy Trails.

Do you have to leave the key in the ACC position to keep the steering unlocked? This is why you pull the accessory fuse....

Huh? What you talking about?