Answer:
Anywhere that electronic processing is required.
They find their way into most domestic appliances, toasters, washing machines, bread makers, irons, hair straighteners, TV, radio, Hi fi. Etc.
They mostly replace mechanical timers and cam operated switches. They offer better funcionality at a cheap price. Having taken the step to use a microprocessor, they can accept several inputs from sensors and finely tune the output, without any moving parts, that can be affected by vibration and/or wear out.