Is it useful to learn how to use a weapon in martial arts?

Answer 1

Yes, for a wide variety of reasons.

Working with a weapon increases the upper body strength. It also improves balance and stance.

Working with a weapon helps one learn how to counter the weapon.

Weapons are all around you. Learning to use one helps provide the ability to improvise. Watch some of Jackie Chan's movies to see him use all sorts of things.

The staff is probably the most versatile weapon. Similar items can be found all over the place such as brooms, mops, curtain rods, garden tools, etc.