1. EXTEND an existing method: call this._super() to run the original code. The example shows calling it AFTER your code is run, and combines it with the necessary return of this (for chaining). But there might be cases where you might like to run the original code FIRST or even in the MIDDLE of your method somewhere.
2. REPLACE an existing method. Just omit call to this._super(). You still need to return this.
3. ADD a new method. Same as (2). You will not call this._super(), as there is no original method to call. You still need to return this.