Blink is a tool that repeats cycled behaviors at random intervals and speeds. It was originally designed for automatic eye-blinking, but it has evolved into a much more general purpose tool.
It works by manipulating a defined cyclic motion, for example the action of a guard in a lookout post lifting his binoculars and scanning the horizon. You could keyframe a 10 second loop of the guard doing his scan, but the clockwork motion would make the character look artificial. With Blink, you can set up that same loop, but allow him to make some scans faster or slower automatically. Even the delay between each scan can be varied.
Blink works on a surprising number of motions. You can make an infinite number of bubbles rise in an underwater scene by defining the motion of just one bubble. Blink will make the same bubble rise again and again, but aperiodically so its motion (and even speed) never predictable. You can make a house shutter bang randomly in the wind. An antiaircraft gun in the background of your animation may periodically fire bursts into the sky. When you have a crowd of people doing warm up exercises, do you really want them all doing everything in exact sync?