This function is not actually utilized anywhere within the library, but I believe it was created with the intention to make it easy to look for messages within a channel that contain certain features without having to worry about the loop running for too long and blocking the thread. I've never actually seen it used before and I don't know why you would ever want to use it instead of calling ->filter directly unless you had a lot of messages in the collection you're searching through.

$collection = $channels->messages->filter(function (Message $message)
{
  return str_contains($message->content, 'hello'); // Adds $message to $collection if it has hello in the content
});

As for why your var_dump is not responding, it is because it is inside of ->done and is losing context. Use a monolog logger and ->then instead.