Before: pair of 3b, well-structured hand

11

22

33

After peng 3b: one less meld to form, but exposed

11

22

33

Peng lets you claim an opponent's discard to complete a triplet. It speeds up your hand, but the claimed meld is exposed for everyone to see. This reveals information about your hand. Peng when it completes a key meld and puts you close to winning; pass when it would leave your hand disorganized.