While I'm inexperienced with GMing, as an RPer I think it depends on the people you're playing with. Some players have a fantastic sense of appropriate timing for their posts, and you can let them have free reign as you know they're both dedicated enough to the RP, and intelligent enough in their decisions of when it's appropriate to post, that they'll manage themselves well. Much of the time, however, there will be at least one or two players who are either too lazy to post without getting a kick up the arse from their GM, or who post every second response in the IC, when there's nothing new to actually say or do. When that happens, you're better off introducing one of the systems above.