@Lengsel On reddit, it was mainly a pre-requisite for who could post or comment. You needed an account with at least X karma to contribute. This would make it easier for mods to ensure quality content, or at least those that put in effort in lower-bar subs before making their way to start a thread to certain subs.
Here, maybe one day, when bots are more of a thing (so, next week), it can be a way to at least prevent some spam, some lesser content, and brand-new accounts from contaminating the masses.
I use it to appreciate a comment with nothing to add, or disagree without having to type a mess. It also prevents me from posting something obsurd that defames me and my profile, that makes me feel like I have a lot of unpopular opinions. It's really just helpful to have a number tell you what a POS or GOD you are.