For various annoying reasons we keep our name change window open much much longer than default. This has led people to make use of it in an interesting manner. Changing your username seems to also clear the post history of a user when you look at their profile. We understood that changing the username would break being tagged in a post but this was unexpected.
I agree that is … not recommended. So our primary reason for a long delay is that when a student registers, generally in spring, with our school we generate an account in our discourse instance. They start receiving the daily digest email at that point as it lets them get to know what is happening on campus. They may no actually start interacting with site till fall or maybe even longer so we have a large window for people to chose their presentation. The other reason is that we have a pretty large Trans population for a college and names and control over one’s own name is of particular importance to them. Which is very reasonable.
Given that people are abusing this we will have to change I think. That said I think it is a little buggy that the post history gets wiped.
Our generally observation, for our setup in particular, is that people want to change their display usernames after they have interacted with the site for a little while. Since we are generating accounts for them and the users are not making an affirmative action to create an account their experience is a bit different than many discourse populations. Sites where the user is making an affirmative action to create their account have a different experience and the users are making a statement about themselves with their display username. In our case that affirmative action is when the user decides that there is enough utility in the site to decide on a display username.
Like I said I was just documenting this somewhere for others.