It's the only way I know how to write, darn it. But I do have a trick that makes things easier for me. Since writing is very hard and rewriting is comparatively easy and rather fun, I always write my scripts all the way through as fast as I can, the first day, if possible, putting in crap jokes and pattern dialogue— "Homer, I don't want you to do that." "Then I won't do it." Then the next day, when I get up, the script's been written. It's lousy, but it's a script. The hard part is done. It's like a crappy little elf has snuck into my office and badly done all my work for me, and then left with a tip of his crappy hat. All I have to do from that point on is fix it. So I've taken a very hard job, writing, and turned it into an easy one, rewriting, overnight. I advise all writers to do their scripts and other writing this way. And be sure to send me a small royalty every time you do it.
Borrowed from @samthielman.com who has sharing restricted - a quote from John Swartzwelder of The Simpsons.
This is also VERY good advice for writing music - get something down. Something complete and functional, then refine it.