For starters datamining my voting patterns for building a deeper interest profile. It should be pretty obvious how this works in terms of user fingerprinting, and the ultimate monetization of Lemmy data. It would be super naive to think that Lemmy will be the one web space immune to this kind of thing. I guarantee you meta already has an army of silent instances doing this.

Worst case scenario, legit state actors use it to target deanonymization attacks.