I am an admitted pantser. I start my stories with no clear idea of where they're going to go or what's going to happen. I've tried writing synopses before but, once I finish them, I find I'm no longer interested in writing the story. I already know how its going to turn out, why would I want to spend any more time on it?
So yes, I start, let the characters dictate the story and reel them back in only when I see they're moving too far off the main story line. How do I know the main story line? I write romance and it isn't hard to find. Boy meets girl, boy loses girl, boy gets girl back. Basic plot line.
And that's probably why I spend so much time with my characters and fleshing them out. All my stories are more character-driven than plot driven. We all know the basic plot. The fun is watching new people, people we've never met before, come up with new reactions, new perspectives on the regular old plot. Remember, there are only 37 plots to begin with!
Although I compose my stories on the computer, I have a spiral notebook with pages dedicated to each character. As decisions are made regarding physical appearance, character traits, likes/dislikes, or any other information that comes out in the story, I write it down in the notebook just so I have a reference to go back to when I can't remember his hair color or whether she said she liked Italian food or that it gave her indigestion.
I also include a timeline of events as they unfold. This serves me well after the first draft of the story is written (my "throwing up" on paper, or the computer screen nowadays). Once the entire story is drafted, I can use the timeline to make sure I didn't leave any plot holes or start a subplot and then drop it partway through. Some people might call this plotting, but since I do it AFTER I've written the story, I consider it an editing tool rather than what a true plotter does.
Does this mean I sometimes overwrite? That I write too much story and have to pare down? Of course. But I like it that way. I hate writing the first draft and then finding holes. I'd much rather write extra and have to condense and tighten up the story. In fact, every single novel I've ever published has a companion folder on my computer called "extras". These are pieces of the story I cut out - sometimes only a paragraph in length - sometimes entire scenes. I throw nothing away.
Later those extra pieces sometimes become stories of their own, like "Secret Signs", a cut scene from Secret Submission that is now included in the Timeless Love anthology. Sometimes I change the character names and they become entirely new stories (Love in the Afternoon). And sometimes they just sit there, waiting their turn.
So...are you a pantser or a plotter?