They are so long that they become content-free. And there are so many that they tend to become spam-ish. I suspect that most people on both sides just skip them. Especially since they tend to look alike, leading one to think that it is the same post over and over. I have noticed that you try to link the topic of the post to whatever the topic in the thread is, but I am not so sure that everybody else does.
I don't think they lead to discussion. It is like someone jumping into the room, screaming for five minutes, then leaving. It tends to stop the conversation.