Well, this is a first I've heard of this. It's not the end of the world provided the pipe isn't getting too hot and you don't mind the continual ash taste.

If this is a daily practice with the same pipe, you might make the pipe sour quicker or risk running a burn out.

I will echo the advice for a cob. You can keep smoking them as they cool down a lot faster and are more disposable due to their low price point.