Writing by hand has always seemed to lead to better compositions. I think its because when you write by hand, you have a deeper connection with the piece. When I sit at a computer and type out the notes, yeah they are mine, but it just doesn't feel as natural.
But when you sit down and write by hand, you have a connection to the piece of music that you would not otherwise have. I do know there have been studies on writing essays by hand vs typing, and writing by hand usually yields better essays.
Another aspect as well, writing by hand I think adds to the learning process when composing. There are feedback mechanisms in your brain that help reinforce what you are writing. For me, this goes hand in hand with not just composing out of the blue whatever you want, but actually composing with a purpose. Specific, targeted composing. Working on things that you are not good at.
My hand goes up for the hand.