In this paper, we examine the value of comments in large-scale discussion forums. We survey the relevant literature and employ the key content quality identification features. We then construct comment semantics features and build several regression models to explore the value of comment semantics dynamics. The results reconfirm the usefulness of several essential quality predictors, including time, reputation, length, and editorship. We also found that comment semantics are valuable to shape the answer quality. Specifically, the diversity of comments significantly contributes to the answer quality. In addition, when searching for good quality answers, it is important to look for diversity in the comments, rather than observing local differences (disputable content). Finally, the presence of comments shepherds the community to revise the posts by attracting attentions to the posts and eventually facilitate the editing process.