When the cue has joint in between, the joint will eat the power when you shoot. The longer the distance bwtween the joint and your gripping hand, the more power being eaten by the joint. So 1/2 eat more power than 3/4 and 3/4 eat more power than one piece.
When you're playing the same brand cue with same quality wood, the one-piece must be better than 3/4 and 1/2. That's why one-piece cue is more expensive than 3/4 and 1/2.