If butts didn't matter, cue makers would be using the cheapest wood for coring dowels and handles.
Why bother with maple and rosewoods?
Just use plywood.
Ah but you could if you did not care about the feel of the hit or how it looked. You can make a gun out of gold and diamonds but what holds the mechanism and barrel won't help you actually send the bullet any straighter or further. It all just helps the person support the barrel better, the barrel and the bullet are the important things. Once the bullet fires, the gun is useless, and what happens to the bullet when it travels and leaves the barrel and flies through the air is what makes it hit the target. The butt just holds the shaft so you can strike it against the cue to do the work.