Why does `{{page-title}}` return `''`?

I'm just curious why the code returns an empty string instead of nothing at all.

To wit:

```js
compute(params, _hash) {
let hash = {
..._hash,
id: this.tokenId,
title: params.join(''),
};

this.tokens.push(hash);
this.tokens.scheduleTitleUpdate();
return '';
}
```

I tried to find if helpers require a return value from `compute`, etc., but couldn't find anything.

Given that, from my understanding, the helper is all side effect (adjusting a part of the DOM outside of its own container), it feels like this helper should have no return value at all.