Originally posted by Lorska:

Remember that you also consume ammo to do something that would cost you nothing or almost nothing if you did it yourself...

That kind of thinking can be applied to almost everything in the game. For example, you can lure a gjall to mountain or cliff side and just melee it. It's not even particularly impractical if you find a good positiong.

Ballista can be used to defend your home autonomously. It does cost resources. Should this not be so? The wooden stake missiles take very small amount of resources, you can use that for small stuff if you wish, and save the black metal missiles (which cause 120 piercing damage btw) for designated enemies like seekers. I wouldn't mind if the latter were a little better though, it doesn't seem like they can actually stagger seekers, but I doubt this is the end of ammunition variety for ballista so in future we can probably load them with elemental missiles.

Ballista is a game feature that is optional and situational. You don't need to use it if you don't think it's worth your time and effort, and I'd advise against anyone thinking of ballista as some sort of universal solution to defense, as Angrybread already explained above. Games are made for audiences of millions, and having every player's base defended in exactly same manner or every character using same equipment would just be boring.

Compare black metal missiles with black metal bolts and you can see they are not expensive at all, even if the ballista is likely to miss on its targets.