Difference between keystohide or scrubber?

It is possible to define your own custom-scrubber, e.g.

Tracy\Debugger::getBlueScreen()->scrubber = $custom_scrubber;

But it is also possible to define an array of keystohide.

Tracy\Debugger::$keysToHide = ['password', /* ... */];

I understand the purpose of keystohide. But what can be the purpose for defining your own scrubber?