Charlie and I (and the other occasional bloggers) rarely talk to each other about what we are going to write about on the blog. My basic rule of thumb is to try to wait at least 3 hours before posting if Charlie has just posted a thread (unless it's strictly informational like a meeting time). And sometimes, I hit "publish" and he has done it at nearly the same time so there's no accounting for that. We don't have a lot of hard and fast rules here.
However, I have tried, gently but firmly, to ask people NOT to hijack a thread and go off-topic for the simple reason that it makes it frustrating for people who start reading only to find the topic started is not being discussed. For me as the writer I wonder, "What happened to the original topic? Not interesting?"
There are a few readers who do this on a regular basis (and even have blogs of their own) and yet ignore this rule. So, just for my own threads, if I see this happening, I'll delete anything severely off-topic. (I completely understand how one thought leads to another and that's okay but if it has absolutely nothing to do with the topic at hand, then it goes.) I'll try to be consistent but I may not always be able to keep up.
I am mainly thinking of trying to keep the threads on topic especially for those who go searching under a certain subject and then they waste a lot of time reading posts that have little to do with the topic. Better fewer posts but linked than a lot of comments that aren't.