According to screenwriter writer David Koepp, who has knocked out screenplays for everything from blockbusters like Jurassic Park to nifty little ghost stories like Presence, momentum is key to getting anything done and done well:

You want to just execute it and have it done, so you can then go back and read it to see what’s lacking. Some days you’ll write seven or eight pages that you just cut the next day because you’re finding the story. It’s part of the process…

Just get it on the page. Write now. Cut later.