Weapons training (kobudo), can be complementary to empty had training in many ways. Like said in the link above, it can help increase balance and satrength and all of those general things. In most martial arts that practise weapons the techniques of the weapons usually are simmilar in mechanics to the empty hand techniques. For example, in Karate, the punch is done with one hand going straight out to the target and the other going straight back into the chamber position. In Kobudo, a basc bo srtike has the same movements, just with a staff in your hands. So, when you practise weapons along with empty hand techs, it can help you gain a better understanding of those techniques.
Also, even if you don't carry your weapons around with you, and i bet you don't, Being used to training with weapons can help you fight against opponents with weapons. You will be used to the different distance of a person striking at you with something.