Terri is absolutely right that every writer finds what works for them. A writing instructor once told me that there were at least two different kinds of writers: gardeners, who tend to let the story grow organically without much advance planning, and carpenters, who painstakingly assemble the story according to a detailed blueprint. I'm more of a carpenter myself, but there are also plenty of successful gardeners out there.
I'm somewhere in between. I outline my stuff and do plenty of concept and backstory notes, but my outlines are often fairly loose and I leave room for figuring out details as I go and discovering new things. I often feel that some of my best work happens when I'm adding or filling in something that wasn't in the outline and I'm just discovering stuff as I go.
And I seem to be relying less on outlines lately. My latest
Star Trek novel had just about my leanest outline yet; since I outlined it for the Abrams continuity before seeing the film, I left a lot of it fairly vague, and I just filled in sequences, characters, and subplots as I wrote, coming up with a number of cool characters and arcs that just emerged with no prior planning. I'm pretty much doing the same thing on the original spec novel I've been working on over the past few months. I wrote the outline for it a few years ago, but I've rethought a lot of its structure since; yet, rather than rewriting the outline, I just went ahead and started writing the book (I was impatient to get on with it) and I've been figuring it out as I go. Which can be tricky, because sometimes I introduce something and have no idea where I'm going to go with it or how it's going to pay off or fit into the larger story.
Though that can produce some marvelous serendipity. For my spec novel, I came up with a technological concept that was basically just a vehicle for providing the initial exposition and setup in an interesting way. But I didn't have any other use in mind for it in the story, so I feared it was kind of gratuitous. But later, I realized that it could provide a solution to a problem I had later in the book, thus making it integral to the story. That actually happens a lot in writing, at least in my experience -- you have two unrelated loose ends and then you realize that they can complete each other.
But of course you can always go back and revise things as needed. There have been instances where I've figured something out about a character in a middle chapter and then gone back to earlier chapters and folded in the appropriate setup for it, so that it wasn't a sudden, out-of-nowhere revelation.