Levers: Hammer weights and travel parameters get amplified or de-emphasized depending on the geometry between keytop and hammer crown. Generally, weight reduction at the key equals loss of hammer rise, and each of the three main levers contributes to this as a give and take. Their relative impact varies, of course, so we benefit by having a well-observed hierarchy in mind as we decide what to try.
We weighoff a key to help its note function properly. With good geometry, good regulation, and appropriate friction in place, key balancing fine tunes how well a note will play. Key weights, traditionally made of lead, offset weight and friction on the back side of the balancerail to aid the player make music from the front side.