When developing a film or TV project, the most fun I have is during the development process, more specifically, the writing. Those of us who are also writers know that this is the stage in which we have the most control over our project. It's just me and my Movie Magic Screenwriter program on my laptop, a perfect symbiosis between creator and medium.
Once you've spit out that first draft, then the real crafting begins...rewriting. You actually have to have something physically in existence in order to mold it to perfection. Think about it. You can't sculpt a statue without the clay and basic shape. So you can't really fix your story without having a first draft already completed.
For example, my movie Cyber Fighter currently in development at JuntoBox Films: http://www.juntoboxfilms.com/projects/cyber-fighter#.UY8_7aJBQ_w
has been rewritten many, many times. In order to perfect the plot, shape the characters, make the dialogue pop, etc. I've needed to periodically fix things that were either called to my attention from re-reading it, or through staged and table readings of the script with writer and actor friends. As the project has been moving forward, I'm also becoming aware of certain elements in the script that might be cost prohibitive. As another example, there was a scene in an earlier draft which had live gunfire. After doing a preliminary budget and schedule to see how this would be done during production, I realized that it was going to get pretty expensive. Plus, the point of the scene had nothing to do with gunfire, there was actually a martial arts fight in the scene as well. So by eliminating the live fire, I was able to cut this scene down to it's essentials, maintaining its moving the plot and story forward while cutting costs. This before a single frame was shot.
Once you're in production, the changes you have to make on the fly are not going to save you as much as the changes you make before you've crewed up and started spending money. Anything you shoot and end up cutting in the editing room is going to be wasted money (even if you add it back as a DVD extra), so it's better to eliminate the stuff that might not make it to the final cut.
One of the best ways to do this is with extensive previsualization. I've mentioned this in an earlier post from 2012 about Zero Budget Pre-Vis, so I won't re-hash. Storyboarding allows you to see your film as it will appear on screen, and you can time this with the script to see the flow. Clunky items can be cut or eliminated, and you'd be surprised at how much you can get rid of and still have a great script.
Even after a successful fundraising campaign, you might not get all the dollars you asked for, so you may need to end up making more cuts to the script so that you can craft a schedule and budget that conforms to the funding. It's always better to do that instead of trying to raise more money when you run out. Always "shoot beneath your means" without sacrificing the integrity of the film.
There's no time limit for development and pre-vis. The longer you can spend on planning, the better you'll be when the cameras start rolling!