I think it's especially important for an editor to say what he's enjoying. For a novelist to be told, midstream, what he's doing right can actually influence the unwritten parts of a novel in a positive way - praise helps a writer know what's good about what he's written, what's interesting and exciting, and what to work for in writing the conclusion.
Donna TarttThere's nothing like having a sympathetic reader who asks the right questions, who understands what you're trying to achieve and only wants to make it better.
Donna TarttFor me - showing a half-finished manuscript is tricky. Just as a bird will get spooked and abandon her eggs if some outside party comes around and makes too much noise or pokes around the nest too intrusively - well, that's what it's like for me if I show work too early and I get a lot of editorial suggestions at the wrong time.
Donna Tartt