I've lifted this from an interview Creative Generalist did with Steve Callaghan, writer and producer of the Family Guy cartoon series. Here is how he describes the process of developing and writing a script.
"Well, as you might imagine, it is a highly collaborative endeavor. There are about 100 people or so who are in some way or another involved in putting together an episode. The process begins, of course, with the writing staff. My fellow writers and I will come up with a concept for an episode and discuss the general storyline that it would contain. The episode is then assigned to a particular writer who will write the first draft of the script. The whole writing staff then takes that first draft and, as a group, rewrites it -- improves jokes that might need some help, fixes any story issues, etc. -- before the show gets recorded by all of our voice actors. Once the audio has been recorded, then our animation team takes the baton, creating an animatic, which is a rough, pencil-sketch version of the show. Once we all screen the animatic, the writers take another pass at the script to address any remaining writing issues. A while later, the show comes back in color. We then do one more, smaller rewrite on the script before the finishing touches (music cues, sound effects, etc.) are added and then you've got yourself an episode of "Family Guy."
Now, compare that with how the typical creative team in the typical ad agency creates their script.
Account person and/or planner explain brief to creative team. They leave. Creative team spend anything from a day to a few weeks sweating it out. They present their ideas to the CD, who says yes, no, maybe, perhaps etc. What is very unlikely is that he will spend any time working with the team beyond this verbal input. Not through laziness, but because the script 'belongs' to the team. Work is then presented back to the account person-planner combo, who are allowed to comment on it, but only within the confines of their job title remit. God help them if they mis judge this and over step into the creatives' domaine. Conversations between planner and account person, account person and client, planner and creative director, planner and client all take place in a isolation to one another. As a result nothing much changes in the script until a director is selected. Now the creative team will listen and make changes, because a) the director is also a 'creative' and b) the team really want to be him.
I've been fortunate enought to have been a part of both processes and I know which one delivers the better work.