Not many folks, developers included, use or know about the oldfashioned interrupts with a system. You mostly see this with embedded systems. Higher end stuff has “messaging” and other methods. But on systems that do not support threading, interrupts can be important. The tutorial below is worth reading about them with arduinos
http://www.engblaze.com/we-interrupt-this-program-to-bring-you-a-tutorial-on-arduino-interrupts/