The answer to this should be obvious. Upgrading your brakes can allow you to stop more quickly, in a shorter distance and decrease fade in racing or heavy, continued use applications (ie canyon runs).
The brake system is composed of the master cylinder, brake fluid, brake lines, discs (also called rotors), calipers, pads and occasionally cooling ducts. And as with other modifications you can spend a lot or a little. A set of pads isn’t too expensive, but if you choose to replace the entire system, you’ll be looking at a couple thousand dollars at least.
What are the negatives? Changing the pads to a more performance oriented pad can result in squealing, increased brake dust (which dirties your wheels more quickly) and decreased pad wear life. Additionally, if you’re unsure of what you’re doing realize that making a mistake on the brake system could cause you and others injury and/or death.
For a complete brake rotor and pad replacement how-to, click here.