The lifetime of a vortex depends upon local meteorological conditions. Vortices last longer in calm air and atmospheric turbulence hastens their decay. It is a question of safety. The rapidly swirling air in a vortex can catch the wings of a following aircraft with potentially disastrous results. Tests with experienced test pilots have shown that even commercial airliners can be thrown out of control if they follow too close behind a large aircraft such as a Boeing 747.
Wake vortices are normally invisible and pilots have no warning that they are flying into one.
Nearly all airline pilots will have had encounters with vortices, usually on the final approach to airports. They are experienced as a buffeting of the aircraft. However, thanks to ICAO regulations on separations, there have been no serious accidents reported with passenger airliners. A better understanding of the wake-vortex phenomenon would permit aircraft to fly closer together when local weather conditions were suitable and so ease congestion. Increasing capacity in this way would be a better solution than building new runways.