Bit of physics.

Energy of a round is completely exhausted when the round stops.

FMJ rounds can go through and through a body, causing damage primarily through penetration, but not all the energy is dispersed in the target.

Hollow, soft nose etc rounds deform upon impact, completely discharging the energy into the target. Theres penetrative damage, but also even nastier damage from they hydrostatic shockwave produced (human body is mainly fluid).

Part of the reason these munitions are banned by Geneva convention.

The counterpoint is that in a close quarter environment, a round that goes through the target has the potential to go through thin walls and cause unintended harm of targets on the other side.