Air flowing over the top of a wing also tends to flow inward toward the fuselage. Meanwhile the air flowing underneath the wing tends to flow outward. As these two airflows meet along the trailing edge of the wing, they form a rotating column of air that extends from the wingtips. This is called a wingtip vortex. These are visible from a passenger's seat next to the wing on humid days, cold, moist mornings or flying through mist.
Energy is lost in the process of making lift because of the airflow around the wingtips.
A wingtip vortex generates a lot of drag. If the lift is spread out over a longer wingspan, the effects of the wingtip vortex are not as great. Engineers have found that designing wings with greater aspect ratio lessens that drag. Aspect ratio is a comparison between the length and width of a wing. Let's do the math.