An atlatl is a device for giving extra speed to a spear. A stick perhaps a foot and a half long
has a socket at distal end for butt of spear. It gives the effect of lengthening throwing arm.
I suspect that most spears were heavy enough that adding weight would be unnecessary.
But if spear shaft were not neavy, and point was not heavy, then addi;ng weight might
increase penetrating power. The pictures of the bannerstones did not look to me as though
they would be helpful. I think the alternate view that they were ceremonial is more likely,
though I can't imagine what role they would play in any ceremony. But so much work went
into shaping them, the creators felt they were important.