Grimrock

What is the use of it, does it will be used at end game, must i carry 20kf of iron balls all the way?

go to the sewers. find the head rat (he doesn't like being disturbed).

note:

The cannon is damaging, but like other guns, the ammo depletes.

cannons are VERY heavy (15kg!).

there aren't very many cannon balls.

all in all, you're probably better off with the rifle you find on the pedestal in the river area, does half the damage of the cannon, but ammo is much more plentiful and it weighs a lot less. you can then have the capacity to carry more bombs, which often do just as much damage as the cannon, and if you are playing alchemist, you can "grow your own bombs", so to speak.

Sweet, as i suspected, it is not essential to the game itself, as i do not use firearm i will drop it, Thank You Very Much! ^^

If you do want to use the Cannon, the item Neck Chain makes it much easier to lug around.