Piano tunings are not quick, nor are they always convenient, but its a necessary discipline to prevent damage. Correct and constant string tension is important to the health of many delicate parts, which are otherwise very expensive to fix. Hence, regular tunings help these parts to work together smoothly, preventing damage to (and from) neighbouring parts.
Over time, the performance of a piano action tends to decline, due to the compression of felt, warping of wood, and other types of wear. A skilled technician can restore it to optimal precision, in a process called regulation, which involves adjustments ranging from turning a small screw to sanding down a wood surface. The goal of regulation is to make the piano's touch and sound consistent across all notes, allow it to comfortably achieve the widest possible range of dynamics, and make the keys responsive to even the most rapid or most subtle motions of the player.