It's possible that you've found this blog and, being so overwhelming impressed by my towering intellect, are dying to know what I think about some pet issue of yours.
Maybe you just want to mention how much you like, or dislike, something about my blog. Maybe you feel like telling me how you found my blog. Maybe you want to mention something, offhand, that isn't quite relevant to anything in particular.
Or perhaps you furiously disagree with me, can't find a relevant post about it, and would just hate for your comment to be unrelated to the post. (In which case, I commend you for your impeccable internet etiquette)
Whatever the reason, this is the place for you! Throw a comment here and I'll respond to it, potentially even with its own post.