When I first started writing I really rebelled at the idea of anything so restrictive as an outline. I used to roll my eyes when writing instructors would talk about the "4 X 6" index card method. I'm not that type of person, I'd scoff (mentally, of course, I mean I AM a Minnesotan.)
Now I can't write without one.
What's changed, you ask. It's not the way I write. Though the outline actually does help reign in my tendency to wander away from plot and go on long, tangential meanders. What having an outline does for me is gives me a sense of where I'm going. If I don't have that, I find sometimes I get lost on the way to the ending and have to do a lot more revision (I still revise a lot, don't get me wrong, it would just be WORSE if I didn't outline.)
I should say that part of the biggest hurtle for me in adopting the outlining method is to shake off that middle school version of the outline, where every detail is structured with a capital "I," followed by a capital "A," etc. Once I realized that I could write an "outline" that was really more like a movie treatment or a project synopsis, I started to be less scared of it.
Because I really was afraid. I was afraid that if I wrote down what was supposed to happen I'd be chained to that vision of the book (or short story.) Instead, now, I think of it as a _possible_ story structure, maybe even the MOST LIKELY, but that the details were still free to be meander and wander and... more importantly, if my characters "told" me to head off in a different direction, I could still let that magic happen.
"But... but... if the outline is that loose, why bother?" you ask. Good question. The answer, for me, is that if I take the time during the pre-writing time to think my plot through to the end, the more likely I am to finish the project generally. Because, for me at least, often the thing that made me sputter to a stop when I wrote short stories or started novels, was not knowing where the h-e-double hockey sticks I was going, you know?
That's my two cents worth. I've learned to stop worrying and love the outline. It's made a world of difference for me.