According to received wisdom on such matters, you’re supposed to write out a description of each of the main characters of your novel. The understanding is that once you know the background to the characters the plot will effortlessly unfold with the inevitability of an electricity bill. I can see the point of this if you’re writing a book like a psychological thriller, a whodunit (although Agatha Christie seemed to get away with cardboard-cut-out characters populating an intricate plot), or even a romance (although the protagonists can often end up stereotyped even there).
The novels I’ve written are thrillers and so involve some fairly detailing plotting and a problem, or several, to be solved – even if the problem is merely a McGuffin. What really matters is the plot, so what about character development? What I’ve found is that the characters develop as you write. I personally hate the idea of dissecting each character and working out what makes them tick before beginning the novel. Not that I haven’t tried it. But I find that the characters still insist on developing in whatever way takes their fancy regardless of what intricate character description I’ve written for them. I think it’s a case of being pragmatic and not too rigid. Sometimes, the development of my characters suggests a plot twist I hadn’t thought of and which, hopefully, enhances the action. Sometimes I need to change the plot because a character has developed in a way that makes the planned action a poor fit.
For example, in my third novel, “Muscle for Hire” the protagonist, Tooley, is a “hard man” from the poor part of Glasgow, Scotland. Originally, I had him winning every punch-up and violent encounter with the bad guys because he was so tough. But that was too one-dimensional. His character turned out to be more accessible on the emotional side than I’d previously planned him. So occasionally I had the bad guys getting one up on Tooley, in order to even up the odds a bit and make it sound more believable.
Similarly, characters change because of encounters with other characters. They have to develop to respond to the situations they find themselves in. So no matter how detailed your character sketches are to start off with, if the character doesn’t evolve he or she can become just another stereotype.
So, yeah, some planning of the characters’ personalities is in order, but to my mind it’s not essential to the process of producing a novel. What is essential is being sensitive enough to the characters that you allow them to evolve as the story progresses. That’s my take on it, anyway.