I tried using this just the other day to find a faintly-remembered old news article about a topic currently in the news. I spent maybe 15 minutes getting nowhere, but noticed that googling for something hypothetically like "tower -trump" would pop up old news articles about the Eiffel Tower on news sites with sidebars linking to current news about President Trump.

The minus operator either no longer works at all, or it just penalizes results without eliminating them.