requires attribute

I have one simple question:

Code:

Ext.define('Packt.store.Menu', {
    extend: 'Ext.data.Store',
    requires: [
        'Packt.model.menu.Root'
    ],
    model: 'Packt.model.menu.Root',

When creating store, there is defined it's model property.

Why use also requires? As I understand, when model is defined, requires is not needed since it also includes requires?

What is the difference? If i remove requires, everything still works.