LLM is incredibly useful as an answer engine*. I can imagine this replacing the Google search box on every mobile device. Why search, browse, decline tracking popups and newsletters signup popups, and then try to fish out scraps of information out of a SEO fluff piece, on a tiny screen, if the LLM can tell you the answer straight away, and answer your follow up questions.
This can be a serious threat to search engines, and by extension information-providing parts of the web, and web advertising (you will be getting ads from your LLM provider, and everyone on the web will hate that their content has been hoovered up for free).
Then we'll have spam trying to manipulate data used to train the bot. There will be commercial spam, but also political/ideological spam. And here's the scary part: to reject the spam, people training those AIs will have to compile a big table of what is true. This will guide the AI that people listen to, and which can be an excellent bullshitter. There is a massive potential for abuse here.
*) the current one is too often confidently incorrect, but that is probably fixable to a good-enough level.