I recently learned that voting on lemmy is not anonymous. Anyone can get information about who has upvoted and downvoted a post or comment.
In combination with your IP, this is a massive privacy (maybe even physical security) risk. Also, people can target you for your votes.
Sadly, this is something where I would prefer Reddit over Lemmy. Big tech scrapes data from both places anyways, at least Reddit is safe.
There is no real “guidelines” about what votes should be used for. Some people use upvotes for visibility, some use it for agreeing. Downvotes are used for disagreeing, reducing visibility, ad hominem, what not.
Even on a personal level, I cannot clearly say what criteria I use for deciding what to vote