SE has a pretty well-defined concept of low vs high quality questions and also answers. See, e.g. this discussion and also this blog entry and also the low-quality-posts tag. The general layout, voting apparatus and community involvement seems to do a decent job of optimizing the site for good questions and good answers. However, although there are general heuristics for deciding whether or not a comment is good or bad (e.g. this discussion and the comment policy), I get the impression that many people in the community feel that comments are largely irrelevant (e.g. this discussion, this discussion and the plethora of moderator-deleted comment threads)
Despite these indicators that the community may feel that comments are largely irrelevant, there seem to exist no statistics about the matter or direct community input on the scale of relevant vs irrelevant comments.
So, do you feel that comments are mostly irrelevant or not? In what ways are comments relevant/irrelevant and what proportion of comments generally fit this description? For example, an irrelevant comment may be irrelevant because it has simply outlived its usefulness, or it may be irrelevant because it was never useful and is either off-topic discussion or rude or etc etc. A relevant comment may be relevant because e.g. it provides "a link to a related question" or because it suggests a clarification in a post and is relatively recent ("should"s from the comment policy).
To clarify, I am NOT asking "what makes a comment a good/bad comment?" as this has been thoroughly hashed out, I think, in other threads pointed out above. The question is specifically about the rate at which good/bad comments are posted/deleted/continue to exist on the SE network. This may take the form of non-numerical input such as "the correct amount of relevant vs irrelevant comments given the nature of comments" or "too many irrelevant comments" or "not enough irrelevant comments I love comment thread off-topic discussion."
Also, I am NOT asking whether or not and when it is appropriate to delete a comment. This has also been addressed in other discussions. This is only about how many comments are irrelevant, and not about what we should do about them.
To reiterate, the question here is how many of the currently existing set of comments, as viewed from the perspective of the present (e.g. previously useful comments may now be un-useful), are relevant vs irrelevant?