To clarify this point a little - I tend to find that once I know /what/ I'm writing and /how/ I'm writing it, it flows out with reckless abandon, and I'm able to get the words out very easily. Due to this, editing also comes quite easy as I find I've written the copy in a natural conversational way (as the article is written in).

However, I realise that this isn't normal, and may also be a big problem when not writing in a style that I can choose.