From Devine Animal Hospital newsletter:
Each year, millions of dogs and cats are lost. In fact, this disaster strikes nearly one-third of all pet-owning families. Of the millions of cats and dogs that are lost, only 10 percent are ever identified and returned to their owners. More pets lives are lost because owners did not identify them than from all infectious diseases combined.
All pets should wear traditional collars with identification and rabies vaccination tags. A traditional collar, however, is not enough. These collars are often worn loosely and are easily removed. Cat collars are designed to break off if the animal is caught in a tree branch. When the traditional collar is lost, removed or breaks off, nothing is left to identify the pet unless the pet has a microchip.