I have to admit that I’ve generally been a “writing by the seat of my pants” type writer. However, more often than not, that’s left me stuck halfway through a script. The past few things I’ve written, I’ve tried planning a bit more – not extensively, but putting down some of the different beats I want to hit.
I’m moving house in a couple of weeks, and I’ll finally have my own study, so I’d already intended to get a large whiteboard to plan things out on. I also have used the Save the Cat! structure software a couple of times, which has been helpful in planning different beats. I don’t agree with sticking with a very rigid formula – “x must happen by page y”, but having some idea of what I’m working towards has definitely helped. I guess that counts as a treatment, but a very much cut-down version. I get bored if I plan too much, but I go completely adrift if I don’t plan, so I’m still trying to find the comfortable balance between the two.
Certainly in a professional environment, where it’s potentially much more collaborative, the planning stages are no doubt absolutely essential. But for spec scripts, it’s a little safer to “wing it”, though like me you could easily get stuck somewhere along the way, or have to rewrite a great deal more at the end of the first draft.