You can build quite an extensive profile of someone given enough post history. More post history means more details. Especially nowadays with LLMs it's trivial. This can lead to all sorts of issues. One is people I know in real life being able to identify me. Another is that through various means my account may be linked to my personal identity (e.g. through matching usernames or emails across platforms) and oppressive regimes (now or in the feature) may use my post history to take action against me.