Clicking a hubwheel on a post puts it in the feeds of your followers. Clicking a hubwheel on a comment puts it in the chatter of your followers.
The hubwheel also influences the sort on a page. More circledots raises the post or comment.
Typically people use it as an appreciation of quality, since low-quality indications of agreement aren't much appreciated by one's followers. Not to say it doesn't happen, but that's the tendency.