Practice makes perfect and you wouldn't want to practice self-defense techniques with the real thing.
From the times of the Roman Gladiators, wooden swords have been used as a training tool. They allowed a warrior to practice full combat safely while preserving his precious steel for the real battle to come.
A practice sword, or waster, is a practice weapon usually made out of wood as it provides an economic and safe option for initial weapons training and sparring, at some loss of genuine experience. A weighted waster may be used for a sort of strength training, making the movements of using an actual sword comparatively easier and quicker. Wasters as wooden practice weapons have been found in a variety of cultures over a number of centuries, including ancient China, Japan, Ireland, Scotland, and into the modern era in Europe and the United States. Over the course of time, wasters took a variety of forms, ranging from simple sticks to careful replicas of real swords.