Like the title says, if you want to upvote something on KBin, you should use the Boost link, not the upvote button (Why? Don’t know…)
The upvote button doesn’t seem to do much, but Boost accomplishes what Reddit’s upvote did. So if you’re looking to encourage a post, use the Boost link.
As I understand it, it’s a feature that is inherited from the underlying ActivityPub protocol which is designed to support all kinds of social network architectures.
If you use Mastodon, their usage makes a lot sense. A ‘favourite’ (upvote on Kbin) is a private thumbs-up to the poster - a pat on the back that has no algorithmic importance.
A Boost is more like a Retweet. Boosting something makes it show up in your followers’ timeline. I guess if you follow a person on kbin, Boosts will do that too and boosted stuff will show on your subscribed home page.