In kenjutsu training there are many types of swords used in the training, all with different goals in mind- truly a sword is never just a sword! Among the wooden types of sword we find a heavier and longer version of the bokken (standard wooden sword) known as a subirito.
With this sword one practices their cuts as the weight of the sword plays against each cut magnifying any deficiencies in your technique. When something is a bit heavier than normal, one has to be extra aware of just how far the cut is going, what the angle of the blade is, etc.
Subirito practice teaches you this in addition to working and strengthening the core muscles of your arms, back, and hips used in kenjutsu.