Why would an airplane pilot choose to intentionally use more runway than required for a takeoff?
Imagine you're doing a takeoff at a high density altitude. You need more runway to get up to speed because your engine is producing less power and you need to move faster to move the same amount of air over your wings as you would at a lower DA.

Aircraft can pretend the DA is higher by using a higher than normal temperature when calculating takeoff information. In jets with automated engine controllers, this setting -in a round about way- allows you to set the engines to produce only the minimum thrust required to get off the ground safely. Since that results in less thrust, there is less wear on the engine and that adds up significantly over time.

Your trade-off for this decreased wear is that you need more runway, which is usually readily available. If you suddenly need full power you just move the throttle to the Take-Off/Go-Around (TOGA) or emergency power setting (or push a TOGA button on the throttle), which overrides the temperature preset.