A modification of this is used when giving a deposition. You want to answer the question without giving any more information than necessary. If they ask about time you say it was after 9 in the morning. You don't say it was 9:15 because you'd just gotten your coffee and had checked your watch.
Yes. In Facebook you could always upvote yourself. I used to always do it when putting the word out about volunteer opportunities where I worked. Not sure if it truly helped but it felt good when the post began with a +2. Not sure if that's something that still can happen there. I've not used FB for much in the past 6 years.
I'm playing with different fediverse at the moment as well as this one. That one doesn't do down votes. Didn't know it at the time when I signed up. The idea is appealing. The idea is that if you disagree with a comment, then you should interact and leave your own viewpoint. An anonymous, unthoughtful down vote does nothing that leads to a discussion. In reddit I'd see something down voted to oblivion because of a name brand mentioned but no discussion as to why people disagreed.
Thus far all of the fediverse has been positive comments 90% of the time.