It seems more and more people are spamming the comment area with a
"+1 for [what you just said that I agree with]"
Is this proper form? If not, could we add an explicit description of not to do this?
AviD explains the reason very well:
To put it simply (and as politely as I can): on average, people are of average intelligence. People like to be heard, and possibly to focus their approval on the one specific part. Or maybe they are hoping to share in the bear greatness of a particularly shining statement by simple repetition, thus granting them too the reflected moonglow of assumed greatness.
More importantly, what can we do about it?
Nice and simple. You don't need to add a comment letting them know it is unnecessary. Mods do delete comments that are obsolete, too chatty, spam, nonsense etc when we see them, but you can help us see them by flagging.
From the canonical meta post, Comments are:
Comments are temporary "Post-It" notes left on a question or answer. You should not expect them to be around forever: Once a clarification has been made, an edit added to the post to include new information, or the issue in the comment is otherwise resolved, it is subject to deletion. In reality, many obsolete or chatty comments remain untouched due to the high volume of comments posted, but this does not mean that they can't or shouldn't be deleted in the future.
It's a vital part of the system, just like posting "-1" comments. The point is to let people know what part of their answer was especially good, to encourage those parts of the answer in the future, both in the answers and others. Remove them, and you will decrease the quality of answers, as people will have to guess what parts of the answers were particularly good
Chances are, if something has been around since the beginning of Stack Exchange, it has a purpose that arguably helps Stack Exchange. Maybe it doesn't actually help, but you can't figure that out until you actually figure out the reasons people do it, and have a broad discussion about the pros and cons. A priori assuming selfishness or ignorance is not helpful.
I personally see no reason that knowing why you were downvoted is useful, but knowing why you were upvoted would not be. I know I've learned a lot from it.
I would agree that this is something that should not be done if you have nothing to say but "I agree." However, I frequently find questions with a top answer that has received dozens of +1's because it was the first answer worthy of a +1, and so during the period when it was favored as a "hot question" without an accepted an answer, people who got to it just a little too late to answer themselves discovered it and decided to +1 it and move on because they didn't have much to add.
But sometimes those answers, while correct and according to the guides and all, are merely "good enough." There may be other answers that are truly superior, or do a better job of leading the questioner to the path of understanding. Sometimes other answers do just as good of a job but additionally they tackle important issues raised in the question that the top answer for some reason didn't respond to. And sometimes there's a morass of answers that are pretty good, and then one jumps out at me as really good for a particular reason.
In occasions like this, I leave a "+1 [because]" comment because I believe that it's possible other intelligent and knowledgeable judges, busy as their type are known to be, just missed this answer when they passed through. As I apply my vote to the answer, I simply want to explain why I believe this answer merited it when there were other answers that seemed to be receiving much more favor. Or I thought the answerer did a good job and wanted to encourage him to continue offering what he can to the community. Maybe others did damn well, but I only have so many upvotes to give in a day. Perhaps it received negative votes from others who didn't explain why, or were unnecessarily harsh, and I thought I could help the answerer improve his offering.
I don't see how these kinds of circumstances don't warrant a comment upon upvoting just like it's important to leave a comment when you downvote to give the author an opportunity to improve his answer, or at the very least do better in the future. When you downvote and take away someone's rep, they deserve to know why (assuming someone else hasn't already told them). On rare occasions, the answerer you're rewarding and/or the answerers you passed over deserve to know why, too.
We upvote answers to show our approval of an answer. We put "+1 for.." in the comments to show our approval of a specific point the poster had made. It is the very same concept, and therefore one very native to the SA behavioral patterns.
When I personally post such a comment, I like to believe that I am helping to improve future answers, and helping readers focus on what I believe important in the answer, therefore improving quality of information on the SA network.
I use +1 in comments when:
I often find great answers that I agree with and want to make some comment on them. E.g., this comment to an answer saying "To protect against padding oracles, you want to make sure that your application does not return a different error when the padding is wrong", where I wanted to mention that if valid padding took different processing time than invalid padding, this could be exploited (even if the error message is the same) and should count as a "different error".
Saying +1 indicates that I agree with your answer and gives the context for my comment. Otherwise, the comment that could be interpreted as a minor correction/pedantic point could be seen as being argumentative like I'm trying to say they are wrong (when they aren't wrong) or forgot/weren't aware of something important, versus just I felt like mentioning something related (though it isn't important enough to warrant another answer).
Tone is hard to convey on the internet, and a +1/-1 helps convey tone in a brief comment.