The generating of maximal power through any punch, will certainly tell ones opponent they mean business, and this will have a profound psychological effect in terms of fazing "the enemy". Indeed, developing power will also help to enhance speed and anaerobic fitness.
Speed will improve as muscles become used to pushing out heavier weights (the cornerstone of any power routine), which translates to a faster punch when the comparatively infinitesimally light, 10-14 ounce gloves are laced on.
Anaerobic fitness, the fitness system which uses carbohydrates to generate short-term, high intensity work, will improve as muscles become adept at sustaining an all-out effort, due to greater lactic-acid-handling abilities (lactic-acid is a by-product of anaerobic metabolism and will prematurely curtail a sustained effort if it cannot be processed efficiently).
If the muscles, which are, after all, conduits for all movement in the boxing ring, cannot function optimally, meaning they cannot generate speed and power, and last the distance, boxing success will be severely impeded. Power, therefore, is a key ingredient in any boxing program. To develop optimal, specific, power for boxing purposes, one needs to pick the right exercises and execute them correctly.