I've always read that extention cords should not be chained. Also one should not build a tree of multi-socket cords. My background is physics, and I cannot see a problem with it, as long as one keeps in mind the current that flows. I might be neglecting something, that's why I want to make sure that I did not miss anything.
In Germany the electrical power is at 230 V, and fuses have current ratings of 10 A or 16 A. On many power strips I've seen that they have a maximum rating of 3500 W. The cable of the extension cord should be specified in a way that it can stand the current of around 16 A.
When using multiple extension cords, there are two fallacies that I can see:
People just see more sockets and connect more and more devices, going over the 3500 W of allowed current. The fuse might not trigger, but the cable will become hot and unsafe. This is something that I can easily avoid as in my use case would only have two nightstand lights and a phone charger at 100 W maximum.
The resistance of the total construction becomes so large that it will become a problem. Especially the DIN VDE 0100-600 seems to say that the resistance of the protective conductor must not be over 0.3 Ω for a cord up to 5 m length. For every additional 7.5 m of length, the resistance may go up by 0.1 Ω. The maximum may be 1 Ω. Assuming that individual cords are according to standard, I could hook up three of them; but that would totally ignore the resistance of the plug-socket-connection.
Where does the problem really come in? Is it that the protective conductor becomes useless if its effective resistance is too large? Or can I indeed chain power strips as long as I keep the total power consumption of that system well below the 3500 W threshold?