I don't use facebook, what is the purpose of like and dislike? Is like meant to signify I agree with this comment. And dislike means I disagree with this comme

I don't use facebook, what is the purpose of like and dislike? Is like meant to signify I agree with this comment. And dislike means I disagree with this comment or does dislike mean I think this comment is bad, O/T, abusive. Or does dislike mean something else. What if you disagreed with the comment, but felt it was a good comment, well argued, well presented and fair etc. would you like it or dislike it? I feel "like" would make it look like you align yourself with the poster, which you may not want but dislike seems wrong too. Maybe overall like / dislike is an indicator of quality of comment, regardless of your personal alignment with the content? I don't get it.