Not encouraging, but supporting it would be desirable.
One specific example where this would be handy is to have a soft launch of a rebranding, where you want to communicate the new URL to search engines before communicating it to the customers.
(Real life example)
Another thing is that a third party can cause a search engine issue by causing duplicate content issues by linking to your home page with arbitrary parameters.
This is caught on every page of a Discourse installation except for the home page - because of the fact that the call to canonical_url is just omitted there. I would make a pull request if I was able to determine the exact code path for the home page…