Thanks @JosephWright for posting! I add my opinion. Quite frankly :-) other opinions welcome.
It's about abusing the name feature for transporting an advertisement, by a single setting that's creating many (thousands) ad copies.
Longer text follows.
Free speech is most important.
Simple promotional (spam) posts though are usually flagged and deleted. That's ok.
We are free in choosing our user name. Using that freedom for web site promotion is a danger for that freedom. Once users such as @user_likes_viagra.com or @user_is_at_bitcoin.cc (fictional addresses) appear visibly, our free choice of user names may be questioned.
Just take a look at the chat of today and see if it's good for conversation to have full URLs in user names in each of their messages and the replies to them, running since some months that way.
So I suggest not to exploit that loophole of putting a web site URL into a user name to reference it in any question, answer, comment, and chat message the user participates. It's like using a tool for automatically adding a URL to any (actual) speech done.
edit: For better understanding, this is, how the TeX.SE chat looks theses days, taken from the discussion that led us here, I highlighted the URL in Firefox to make visible how speech space is taken and what my brain has to skip each time, while living with the awkward grammar/sentences as result of combining with _is_at_longURL and likeslongURL:
An irony is, that the URL is rarely shown on the names in the left side, but those longish statements are automatically inserted when I reply to people, that's why you see me involuntarily repeating the web site name here.
Sorry I don't have other web site promotion in name examples as this is the only one I know as currently happening. And I want to show how the actual effect in chat looks like. I would like to show something like kind of a @user_likes_viagra.com example but that spam doesn't happen. I show this to explain my point about web site statements in names and chat handles in general, as in the beginning of my answer.
It's a 5 months ago planned promotion. Now, see my screenshot above, it affects the TeX.SE chat experience too much for me. Not only that promotion text copies are there sometimes piling up.
It may be commercial promotion, political promotion, religious promotion, or yelling about persons or communities one does or doesn't like.
That technical way of unsolicitedly putting promotional statements via the reply user handle into my speech, is affecting my free speech. Yes, I click on reply and that promotional statement with web site name is inserted at the beginning of my speech. And I can't shorten that statement with the backspace key.
It's not the intended us of the name feature. This and the sample depiction is just my opinion as contribution to the views.