Preview doesn't come out in format. You sometimes don't notice your mistakes until after you have posted (spelling and grammar) Often, when using the post as a palette, you sometimes glean a different way of wanting to say something after you've said it. That can sometimes take more than five minutes. This post box is very small, so you can only see 5 lines of text at a time anyway, the post itself is presented in one big box, and the effect of typing and then reading what you've typed are often two discreet things.
This is at the core of my "three post style", actually.