Are there still flash mobs or swarms or whatever ya call 'em? Everybody shows up at one place. Like vultures smelling dying flesh? Why?

I never understood the robotic response of tons of folks going hither and yon to show up at some last-minute appointed place. To feed off of what? One another? What is the value of SWARMS of anything? Locusts or bees or ants or humans or Zombies or thugs ? They dutifully follow orders to be somewhere at a set time and obey they do. So once there what happens? They all giggle and smile and dance or rush off to another place so they can giggle and dance and then rush off to another place? Seriously? WEIRD.