This is a very interesting thing about how people become great writers. It's a lesson I never forgot. The writer Hunter S Thompson once said that he would retype entire novels, just to get a feel for what the writer was thinking, to understand the method and the prose as each word follows.
This is a lesson in greatness I think. When I started joke writing, I would write out a joke word by word and then take it apart. I would consider how important each word was in relation to the joke. It's something I'm still doing and has taught me the patterns, the turn, the punch, the changes. I feel like typing something out forces someone to pay a very close and detailed attention that wouldn't come simply from reading.
When Georg Büchner translated Hugo's plays, I think that would have been a great and invaluable lesson in writing.