The age-old question: Should a novelist outline or not?
Well, I do both.. I prefer to write "organically" to get to know my characters first and chances are they do kind of wander and I do have to eventually trim and cut... but it helps me tremendously to get to know my characters, and that in turn leads me to discover the plot -- did I mention I write character-driven stories? Mostly.
With my current WIP, I wrote about 40K without any outline at all, just a general concept in my mind. But then I came to a point when I drafted out a skeletal plot structure so I know where I am going with the story.
I do have what I call "set pieces" or guideposts and an ending in mind (which, of course, may change over time) so I don't wander too far. I always use the analogy of taking a road trip: I know I am going to start from New York, and will end up somewhere near San Diego, and I would like to visit X, Y and Z and I know my general direction (the southern route instead of the northern), but as far as the journey is concerned, I don't have a set itinerary. And maybe eventually I will have to skip Town X but manage to see Town A instead... and maybe eventually I will end up in Los Angeles instead of San Diego, but close enough...
That's how I manage to have my cake and eat it too, by having a flexible skeleton of a plot but continue to let my characters dictate how they're going to get to the end.
When I start on my thriller, I'll probably take a more plot-driven approach... we'll see.
The way I look at it: whether we outline or not, we're pretty much doing similar things, just different approaches. If you write by the seat of your pants, you may end up with a first draft that is 70% complete -- this would become your outline! Then you rework it. On the other hand, if you outline everything up front, you're basically doing a 5-10% first draft, without much actual writing. The notes, the charts, the plans, etc. are all part of this 5% draft. Then when you're actually writing, you're really writing your "second draft" as the non-outliners would call it.
At least that's the way I look at it. Either way, you'll sooner or later end up somewhere. You have to do what is right for you -- some people prefer to have a 70% first draft, and some prefer the 5%. Whatever works, baby.