Writing: To outline or not to outline?

IMHO, there is no question about it. Writing an outline and/or a treatment gives you some sense of where are you going, how you will get there (eventually), and, most important of all, give you some idea if you are on the right track.
I even wrote an outline for the Unix/Linux Survival Guide [en|de]. It is non-fiction, granted, but I still needed to know where I'm going and how to get there, a blueprint if you will. Writing non-fiction does not need an outline or treatment. If so, how do you sell the idea to someone? You have to come up with more than an idea to convince a publisher to publish your works (maybe Dan Brown does not have to do this, but still...).
Why am I writing this? Because an article on The Artful Writer called This Argument Really Does Have A Right Answer showed me, that I am not alone with this mantra. (Not that I needed the reassurance.)
;-)
BTW: Wether you call it outline or treatment is kind of a rhetorical question, use whatever works best for you. I will expand on the subject in a later post.