Nah, it's just to avoid having to have two lines for every variable, i.e.

```js
beforeEach(function () {
    this.timeout = setTimeout(doStuff, 1000);
});
```

instead of

```js
var timeout;
beforeEach(function () {
    timeout = setTimeout(doStuff, 1000);
});
```

They multiply pretty quickly so the `this` technique helps; indeed I thought that was the reason you added it to Mocha in the first place.