computed option allows you to do something to your data on the fly. You can transform your data through a computed property, which reacts to the changes on the data to perform an action.
This is part and parcel what makes vuejs components reactive.
Some use cases in the real world are calculating percentages for dashboards, styling css animations, or using an auto-complete/type ahead system, or form validation.
To use a computed property, we make a function, which gets called when some piece of data changes, and to get that changed data, we call the name of the function in the DOM to get the result.