I've written on writing in the moment before but I want to add something about my process here.

One thing that was important for me to learn is that writing fiction is juggling many things at once and not thinking about any of them while you’re in the act of writing. There are just so many areas of concern: voice, character, plot, setting, language, and on and on. If we think about them while we’re writing, there’s a good chance we’ll freeze up or go into a kind of stiff, forced writing, or maybe make the wrong choices. And the wrong choices can be deadly in a novel. The wrong choices can lead you to other wrong choices and then you’re halfway through the novel and you’re thinking, HOW THE F**K DID I GET HERE? WHAT AM I DOING HERE? THIS ISN’T MY BEAUTIFUL NOVEL. THESE AREN’T MY BEAUTIFUL CHARACTERS (and before you know it you’re in a Talking Heads song—sorry, off topic). 

So--you can't think--much--about writing while you're writing. You can think all around it, of course. When you're driving your car (this, of course, does raise safety concerns but we all must make sacrifices for our art), taking a shower, walking the dog (one of my favorites). I'm constantly turning over aspects of what I'm working on when I'm not actually working but the writing itself, in my opinion, should be as much in the moment of the story as possible.

So yes--writing in the moment is important for making the right choices and discovering connections between plot and character.

But the thinking that goes on around the writing process is important too.  Lately, I've been trying to order this thinking a bit more by writing it out. I'm not yet ready to call it an outline but it is brainstorming in a more orderly way.  I've always been a discovery writer so this is a bit new for me. More later on how this works for me--for now I just want to point out that I think that you can be a believer in discovery writing (finding your way by writing it out) AND mapping aspects of story and character in order to guide some of these discoveries.