Since air goes from higher pressure to lower pressure (which creates lift), air is also going around the wingtips. This causes a whirlwind effect with fast moving air forming a vortex. Wingtip vortices can pose a hazard to aircraft, especially during the landing and takeoff phases of flight.
To reduce wingtip vortices, manufacturers install winglets at the tip of the wings. This causes the circulating air to be disrupted and the air to dissipate. This also causes less drag for the aircraft which improves fuel efficiency.