It means he agreed and upvoted, but didn't have anything to add. It's not actually much better than just upvoting, accept it creates a response vector where the person you just upvoted can easily return the upvote.
Not a fan personally, but I'm not the +1 police.
You got me - its just a cheap way to make more comments. )
People will always find a way to get a comment added so others could possibly upvote the comment, therefore generating profit for them making a worthless comment.
Me, I try to give people someone to read first before I post.
+1 on that @josephsavage ;)
Oh never knew that. Thanks for the explanation
It originates from big e-mail threads (and other platforms) where there weren't any likes or upvotes. It used to be (and often still is) the way to say one agrees. It wasn't always a way to farm free money :)