
Well, for one, conflicts keeps the story and, more importantly your characters, moving. If nothing happens, your characters have nothing to do. They just sit around and stare at each other and the reader, wondering why they are there. Horrible (or not so horrible) things happening, keep the story moving forward. They work as the ultimate motivator for pretty much everything.
When I say conflict, I'm not just talking about the central conflict of the book. Take your standard Hero character, for instance. Conflict surrounds him/her. There was a tragic incident in their childhood/recent history/right before the book started, and conflict continues to follow them for most of their journey. It their motive - that is, finding resolution to the conflict often times, in one way or another, carries the story through to it's lovely (and sometimes not so lovely) conclusion.
So when you write, always remember to ask yourself - what is the Great Problem/Central Conflict that drives the plot forward or motivates your characters? Even if it's something that affects only the main character, if it's conflict, you are on your way to making a coherent and movable story.
What about you guys? How important is conflict to you and your story?