[JamesBarney]

When I'm still prototyping I usually pick the part of the project I am the most uncertain about, then write a big function with lots of anonymous types. Once I feel more familiar with it I refactor into types.

But types can also be really useful when you are in the process of learning your domain. If I'm using javascript and I realize I could better represent my code if I did some refactorings I usually don't touch it because I fear breaking something. On the other hand if I'm using a statically typed language I feel free to refactor to my hearts content with the knowledge that the chance I break something is far smaller.