Refs versus State
Since refs can be used to get quick and easy access to DOM elements, the question that might come up is whether you should always use refs instead of state.
The clear answer to this question is "no".
Refs can be a very good alternative in use cases like the one shown above, when you need read access to an element. This is very often the case when dealing with user input. In general, refs can replace state if you're just accessing some value to read it when some function (a form submit handler function, for example) is executed. As soon as you need to change values and those changes must be reflected in the UI (for example, by rendering some conditional content), refs are out of the game.
In the example above, if, besides getting the entered value, you'd also like to reset (i.e., clear) the email input after the form was submitted, you should use state again. While you could reset the input with the help of a ref, you should not do that...
