I believe there's two kinds of writing: no plan and planned.
For most of my works, at least the more creative ones, I usually have no idea what's going to happen next. And with that freedom I can allow my characters to breathe and be, well, characters. That's why whenever I do outlines because I often feel like I'm constricted and I really never get anywhere since I'm so concerned with where I need to go rather than allow the characters get there in their own way. The most I plan is the concept, how the characters interact, and a foggy idea of what the ending should be like. But otherwise I just go for it.
And if I let myself go, I'll write. A lot. And my worries of what will happen next are not usually a problem. However, there's a downside to this sort of storytelling. If you hit a wall and you have no idea where it can go, you're REALLY stuck.
But then there's the planned route of story. You make an outline, you know what the characters are like, and you have most of the details written down. Now you just got to get started. Because you have an outline, it's like a map. You have a destination. An idea of where you need to go. In this manner, you can get to the end of the story and move on to something else.
But once again, there's a problem with this too. There are stories that I've read or even written that followed an exact outline, and in the midst of reading, I felt that the writing was a bit too calculated, almost robotic. The writer (including myself) had a constraint to their words and their worlds. This seems to happen a lot in movies as well.
So, I say there should be a happy medium between the two. Have a plan of action (an outline), but don't be afraid to change that plan of action if the characters or situation are out of character or situation. That way you can avoid those "deus ex machina" moments that everyone gets stuck on. And, you have both freedom and a more defined goal.