They create a "story drift" that is hard for users to escape. Many users don't – and shouldn't have to – understand the nature and common issues of context. I think in the case of the original story here the LLM was pretty much in full RPG mode.
I've turned off conversation memory months ago, in most cases i appreciate knowing i'm working with a fresh context window; i want to know what the model thinks, not what it guesses i'd like to hear. I think conversations with memory enabled should have a clear warning message on top.