With posture we have more power, it’s that simple. Can we keep that power while fighting? Untrained fighters lose posture right away.
If someone attacks us and we lose posture, it’s over.
If we fail to keep elbows in tight, it’s over. With elbows out we won’t cause damage, and they break our arm or take their choice.
Elbows in is something we have to practice. Elbows out is the same as knees caving in jumping/landing. They both lead to injury and loss of power. With power we injure them.
Spend a few minutes on your own, then find a partner to play half speed. Throw slow shots, feel posture and elbows. Next add simple footwork in, and keep breathing.
Breaking some fool could save your life.