The Big Switch is a smartapp under MORE that allows you to specify that one switch/bulb will follow another. So when bulb A goes on, Bulb B goes on, and so on.
@tslagle13 wrote a modified version that lets you trigger a Hello Home Action when a bulb/switch goes on or off. This is called “Big Switch for Hello Home Phrases.” So now when Bulb A goes on, Hello Home Action X runs. This becomes a very easy way to have a bulb/switch going on or off trigger all kinds of other things, anything you can put in a Hello Home Action.