sultanoswing:
If a car can skid when you hit the brakes hard, then the brakes are adequate, and it's the tyre grip letting you down.
That's fine for a single stop, but takes no account of the cumulative heat from repeated or lengthy cycles or the extra energy to dissipate from towing. Those same brakes that will let you skid for one stop might do nothing at all after the first few bends on a twisty downhill road with a trailer on. An important aspect of brake performance is repeated stops in short succesion, which is where better ventilation/cooling is very important.