The overwhelming majority of edits never get discussed. There are articles' discussion pages. There are also individual user's discussion pages, where you might post something like "Why did you do this particular edit?" and a discussion might ensue. The user page is usually a more appropriate place when the user has done only one small edit to the article and may not be watching it. (Click on "history" and you see the article's edit history, including user names of logged-in users who've edited it, on what date they edited, and the content of the edit if you click on "diff". In addition, when looking at a user page or a user-discussion page, you can click on "user contributions" and see a list of that user's edits in reverse-chronological order.)
However, there are also discussion pages of WikiProjects. A WikiProject tries to bring together people interested in developing and improving Wikipedia articles on some particular subject, e.g. biology or Protestantism or chess or ancient Greece or poetry, etc. Each WikiProject has a project page describing what the project is about and a discussion page. On the discussion pages, one might talk about articles in general (Should we put our standard template at the top or bottom of articles on ABCology? How much prominence should we give to biographies of influential ABCologists?) or about particular articles (Is this an important enough point to warrant a whole section in the article about that?). An article can be within the scope of several different WkiProjects. For example, "Ptolemy's table of chords" can be within the scope of the projects on (1) astronomy, (2) ancient Greek writers, (3) mathematics, (4) history of science, and (5) Egypt. "Lake Superior" could be within the scope of projects on (1) geography, (2) environmentalism, (3) lakes, (4) North America, and (5) geology. In some cases, a posting to discussion pages of WikiProjects may be more appropriate than a posting to an article's discussion page, because the latter may not get attention from very many users.
I sometimes post to the page titled "Wikipedia talk:WikiProject Mathematics." Being accustomed to that page, I'm sometimes surprised when I post to another WikiProject's talk page and don't get a reply for several days. The math project's talk page is quite lively; some others are as well, and some are not.More questions on Wikipedia: