Its weakness is that once one becomes lighter, they are unable to put the same amount of force into their attacks.
Contrarily, by increasing gravity, it becomes harder to move, but you can put more force into your attacks.
Another disadvantage is that it can’t differentiate between friend and foe. An interesting use is that if an enemy is sent flying, it can increase their impact, and if you are sent flying, it can decrease yours.
There’s no question why this was such a difficult material for the Old Man to make a weapon out of.