|This article is about the current version of DF.|
Dwarves won't harm each other (or themselves) during combat drills, or sparring while using metal weapons, so training weapons are only useful when you have no metal weapon of the kind you'd like your soldiers to train with, and in a few specific circumstances.
Training weapons are useless in combat, so make sure that your soldiers have exchanged them for real weapons before sending them into battle, even if it means using a weapon they are totally unfamiliar with. Their utter uselessness can prove useful for live training, however.
Note that soldiers equipped with training weapons for extended periods of time can grow attached to their worthless wooden weapons. Congratulations, you now have a legendary stick.
Training weapons also have a few specific applications: poor-quality training spears are a prime component in danger room design. Training axes used to be used as equipment for tree cutting, freeing up embark points for other supplies but this bug was fixed in 0.43.03. Training weapons can also render your fortress guard harmless to any unfortunate criminals.