Terminal ballistics is much like drag racing, but in reverse. The more "horsepower" (energy) that can be adequately transferred to the distance within the animal's vitals, the more damage and quicker kills.
Bullet blowup can be compared with excessive wheel spin in drag racing, while inadequate wound channel is caused by too little "horsepower" (velocity & mass) and/or too little bullet expansion. Adequate deceleration within medium game results in the bullet expending nearly all it's energy, while retaining enough to cause an exit wound. Expansion acts like a drag-chute, slowing the bullet more quickly, transferring more of the bullet's energy to tissue instead of anything beyond the animal.
Choosing a proper bullet is more critical when using smaller calibers than, say .308-.35 calibers, because they need to expand more than the larger ones and retain a higher percentage of mass to achieve the same killing power. Blowup and shedding of bullet particles are detrimental to deep energy transfer.