The short answer is never. This might not be as satisfying an answer as some are after, but i think with proper qualification we can start to see why it is the case. The efforts of this project of etiquette are and will continue to be to sift through the vast body if literature on the subject and end up with those few essential elements of gentlemanly conduct that truly matter. That being said there is a great deal that can be discarded along the way. These would be things like throwing your coat down over a puddle to save your lady’s shoes from getting wet or bowing to your superiors (while in North America). It is the very basics of gentlemanly behaviour that we want to have internalized so that we can rely on it like a second nature.
A great way to illustrate this is with personal hygiene. This is something one participates in both in the public domain and when at home with no one else around. But what does this have to do with etiquette? Hygiene affects you first and foremost. If you were to never bathe of brush your teeth it would only be a matter of time before you caught some cold that you would be less able to fight or started to develop cavities in your teeth. If you were to stay at home by yourself at all times this would only affect you, but if you went out in public you would be putting others at risk of catching whatever it is you are sick with (excluding cavities of course). No one in the public domain is aware of your lack of good hygiene and they certainly ask you to get them sick. On the other hand good hygiene avoids all of this and it is something that you do for yourself primarily but for others indirectly. It is my belief that etiquette works in the same way.
Etiquette is something that must be cultivated and practised at all times. This sounds like a great deal of work, and it is, but like a great many things the more you do it the easier it becomes. So what, you ask, is an example from etiquette that fits this analogy? Lets start with respecting others. There is only one way anyone can properly learn what respect is and how to show it to others: that is to respect ones self. This can be anything like hygiene, exercise, a healthy diet, education or responsibility. These are all things that you must cultivate in yourself in order to fully appreciate both yourself and those around you.