What should I use it for?
In case of posts - should I downvote things that I don’t agree with? Or things that I don’t want to see in my feed (posts with low amount of votes fell more to the bottom)? Or things that I consider harmful/stupid/younameit?
In case of comments - should I downvote something that I don’t agree with? When should I use this button in case of comments. Or maybe I should not - cause what’s the point, actually?
Not true at all. This is how it was written in the Reddiquette from the beginning, and for some time, it was used like that. Today, though, it’s absolutely like you say: It is only used for agreement and disagreement, or “whooo I like that!!1” and “booo I hate that!!1”.
Though they still incorporated these old rules in the new version of the Reddiquette, they do practicall nothing for getting these rules known to the users. If you ask me, they can sell the data they gain from the voting system way better if the data stems from emotional reactions rather than thoughtful analysis.