Each time I ship something, I'm discovering that I could have cut things down much further than I did and saved (months/weeks/days) of effort, and just wasn't ready to believe it in the planning stages.
Plus, moving fast gives me more opportunities to work on marketing skills and gain some real experience there. Project artifacts have zero real value until someone is using them, so the marketing effort is a way to mitigate risk, and shouldn't be an "oh my god did we get it right?" shuttle-launching kind of experience. If you feel like it's a shuttle launch, you may have taken on too much risk(for a web app).