Bedding allows your brakes to reach their maximum potential. Until they are bedded, brakes will not work as well as they are able to. If you've installed a bigger brake kit or you have changed pads and discs, you should always bed the brakes. Proper bedding improves pedal feel, reduces or even eliminates brake squeal, reduces brake dust and extends the life of pads and discs.  

Immediately after installing new pads, discs or a big brake kit, the first few applications of the brakes will result in very little braking power. Gently use the brakes a few times at low speed to build up some grip before going up the road at high speed. 

If you just installed brake discs with zinc plating or if the brake discs have an anti-corrosion phosphate coating, you should postpone bedding until normal driving has allowed your pads to polish the discs clean and removed all traces of the plating or coating.  If your new brake discs have an oily anti-corrosion coating, clean this off thoroughly with a brake cleaning spray or hot soapy water before installation.

From 60mph, gently apply the brakes a couple of times to bring them up to operating temperature.  This prevents you from thermally shocking the rotors and pads in the next steps.

Would recommend doing eight to ten near-stops from 60mph to about 20 mph. Do it HARD by pressing the brakes firmly, but do not lock the wheels or engage ABS.  At the end of each slowdown, immediately accelerate back to 60mph, then apply the brakes again.  DO NOT COME TO A COMPLETE STOP!  If you stop completely, with your foot on the brake pedal, pad material will be imprinted onto the hot rotors, which could lead to vibration and uneven braking.

The brakes may begin to fade after the 7th or 8th near-stop. This fade will stabilize, but not completely go away until the brakes have fully cooled.  A strong smell from the brakes, and even some smoke, are normal.

After the last near-stop, accelerate back up to speed and cruise for a few minutes, using the brakes as little as possible to allow them to cool down.  Try not to become trapped in traffic or come to a complete stop while the brakes are still hot.

After the break-in cycle, there should be a slight blue tint and a light grey film on each rotor face. The blue tint tells you the rotor has reached break-in temperature and the grey film is pad material starting to transfer onto the rotor face. This is what you are looking for.  The best braking occurs when there is an even layer of pad material deposited across the rotors.  This minimizes squealing, increases braking torque, and maximizes pad and rotor life.

After the first break in cycle shown above, the brakes may still not be fully broken in.  A second bed-in cycle, AFTER the brakes have cooled down fully from the first cycle, may be necessary before the brakes really start to perform well.  This is especially true if you have installed new pads on old rotors since the pads need some usage to conform to the rotor wear pattern. 

If you've just installed a big brake kit, pedal travel may not feel as firm as you expected.  After the second bedding cycle, the pedal will become noticeably firmer.  If necessary, bleed the brakes to improve pedal firmness.