I second this as a way of working. I think the line from brain to arm to hand to pen to paper gets first thoughts down so much easier. (Also no annoying red line squiggles when you make spelling mistakes and typos.)

Also you can write longhand anywhere - on public transport, in cafes/bars/restaurants, in the bath, in bed, watching TV with an ease that even a laptop doesn't always allow.

And moving from one working method to another for that first edit helps as well, I think. When I am reading and typing out that first draft, I think it's easier to notice where I need more action or explanation or dialogue.

Also I must be one of the few people left who can handwrite faster than I can type. :( There's a reason my default icon is a fountain pen.