Brakes work by converting the energy of the wheel hub spinning, into heat. However the tires must first convert the energy of the car moving forward into the energy of the wheel hubs spinning.

If you lock the wheels or get the ABS to kick in, that means the tires are not able to enough convert forward motion into rotation for the brakes to convert into heat. This also means that the tires have no traction and are doing not much at all to slow you down.

If you increase µ (coefficient of brake friction), you increase the brakes' capacity to convert motion into heat. Generally a pad with a higher µ will also have a higher tolerance for temperature. Increasing µ will give you better inital bite and more fade resistance but it will not stop the car any sooner with the same tires.

If you increase tire traction, you increase the supply of energy for the brakes to convert into heat. That works the brakes harder which in turn means you can use a pad with a higher µ to take advantage of the larger supply of rotational energy given by the stickier tires.

Make sense?