If you can make a point in a couple seconds, do it!
If you are not satisfied with 5, 10 or maybe 20 seconds of my time, then you are asking me to sacrifice a lot, and to trust you very much. Why should I trust you?
If your document spans several pages, do you really think I will be impressed at the end of it? If not, then please do us all a favor and keep it to yourself!
Otherwise, I might get the impression that I had to sit through several minutes of waffle simply because you were afraid you would never be able to captivate me again. If that rings true, it probably is.