I think most people who plan ahead also plan the twists and side-events though. I know I do. I plan ahead. If I don't, what I end up with is just crap that isn't going anywhere. Even if I have a vague idea, I need to write down the plot as a whole to see that I actually have a story. Main reason for that being that I come up with new stories all the time, and can't be wasting time on one that won't go anywhere. The plot might change many times if I think of better things, but I always let new ideas (and new plots) simmer for a bit before using them.
Jeffery, I'm with you. But I also know the minimalist approach isn't for everyone. I prefer the flexibility of not trying to nail everything down in a prefabricated plan. For me, it makes the story flow more organically. But many other writers need to construct a roadmap before they begin writing.
My way of writing is like planning a trip; Lets say NY city to Indianapolis, I want to stop at certain places along the way, so I get a general idea of how I want to go, and then I get started. I might find interesting things along the way, that were not planned. But I don't plot every single road, each gas station or rest stop. You want to have a direction, a destination, but not a rigid unchanging plan during the trip. And ignore that GPS voice that tells you not to venture away from the plan either.