I would think that a composer of any talent would know (or find out soon enough once he's started writing) whether or not he needs to work things out on paper or not most of the time. If there is an established groove that things are going to be layered over then why write it down? Conversely you could construct the groove in midi and then compose a highly polyphonic four part texture over it that would only come together if carefully composed on paper. A less complicated polyphonic texture however could be put together without writing it down.
I think I'm saying that one should use the most effective technique in order to achieve a specific sound. Many film composers today just don't have real composition chops like Williams or Goldsmith or Herrmann or North et. al. So they don't get that particular sound that only comes from a certain compositional/structural integrity. If your not after that sound I wouldn't sweat it. If you are then writing it down is probably the only way. I would site the Fuge in Jaws or the Passacaglia in The Blue Max as extreme examples. These things are the result of real hard writing that would (I think) be more difficult if not impossible to do with a midi approach than on paper.
I think I'm saying that one should use the most effective technique in order to achieve a specific sound. Many film composers today just don't have real composition chops like Williams or Goldsmith or Herrmann or North et. al. So they don't get that particular sound that only comes from a certain compositional/structural integrity. If your not after that sound I wouldn't sweat it. If you are then writing it down is probably the only way. I would site the Fuge in Jaws or the Passacaglia in The Blue Max as extreme examples. These things are the result of real hard writing that would (I think) be more difficult if not impossible to do with a midi approach than on paper.