I agree with Keith. In my experience the use of tsuba depends on what
and with whom you're training. Your sword teacher should be able to explain and demonstrate why you need a tsuba or not. Even within the same style, you might find that for some parts of the curriculum you use bokuto with tsuba, for some you don't (different bokuto, no tsuba). It depends on what you're training. Some training is inherently more dangerous to the hands, or might need a tsuba for other reasons. Then again sometimes you need to put on some armor to train certain things at a certain level. I've had a bunch of those cheap plastic tsuba broken... better than breaking my fingers
. I have a bunch of plastic tsuba in my bag, I just replace them (maybe I need to get a fancy leather or metal one).