Why use a dog crate:

When used correctly, dog crates are the fastest and way to housebreak your dog. Dogs are naturally den animals and naturally want a small, cozy place to rest for shelter and security. Dogs naturally want to keep their den clean and unsoiled. Crating your dog teaches him to "hold it" until he can go in an appropriate place.  This helps your puppy develop his bladder control.

For older dogs, crates act as a "bedroom" where they can relax and escape when there is too much activity going on around them. You can crate train a dog of any age.  A crate can help break bad habits that improperly trained dogs may have developed over the years.