Tony, thank you very much for that detailed comment! I really appreciate it!
Though I'm now able to read those chapters of the Mastering XPages book I always felt more convenient using the "loaded" property to compute the usage of a component (e.g. a custom control). This was just a feeling and was caused by the simple translation of the words "loaded" and "rendered". What is not loaded doesn't bother me (and the system) at all. But your statement confirms that my assumption was right regarding the phases of the JSF/XSP lifecycle.
So I might be right to thank you and your team who created the XSP above the JSF layer for adding the "loaded" property on top 