I fully agree about the new system, as i already mentioned earlier in the thread. In that regards, let me quote the OP:
Thank you, FD!
All my comments below are related to the state of affairs before this new system was implemented.
So...
A random system out there with random ordinary objects there - who cares? It doesnt matter if you tag everything or nothing, nobody will pay attention. But imagine you spot something shiny on the starmap. A very rare type of star or nice planetary nebula. Anything which is rare and thus valuable. You set sail, travel many ly and when get there...it is tagged. For most explorers it is a disappointment. As you mentioned, we are not tourists, visiting whatever somebody else has discovered long time ago. We want to be the ones who make the great discovery. And here comes the etiquette part. Most explorers i know tag the main star and the most interesting objects. But leave the rest for those who come after them. It is a gesture of politeness and explorers solidarity. Cmdrs have traveled thousands of ly (sometimes) to get there. Dont leave them with empty hands, let them have one of those insignificant moons. You wouldnt profit too much by scanning icy moons anyway, would you?
Thats why all over the galaxy in many of the most interesting systems you can find the tags of several cmdrs.
Yes, it is an unwritten rule. It is up to you to decide whether you want to make a gesture of politeness and good will to those who come after you or not.
To avoid any misunderstanding, once again: the new system makes all this irrelevant in many cases.