It's good if you really don't want your LLM to mention specific things, which I can see some groups wanting. Having it mention some things even when they're not related could be good for integrated ads in a chatbot, which sounds evil in that it would be really annoying. Your friend's account gets hacked, a chatbot LLM is finetuned on their message history, it's able to carry on a conversation while slipping in a mention of Joe's Hot Dogs every now and then.

It probably also could help with consistency when trying to do LangChain-type stuff.