Personal testimony from working with Roz:

I had an old short story (written in the late 1980s) that I knew could use some work. Roz walked me through overall problems and specific problems; things I would need to do to make the story better. Then she dropped the big one: "Right now, I have no emotional connection at all with your two main characters. I don't really care if they succeed or fail. You need to establish that before the story will work."

Woah! Roz, you don't like my characters?! They're... actually, y'know what, now that I think about it, *I* don't like my characters. One's a self-rightous jerk and the other's a psycho. Do I want to spend more time in these people's heads to improve the story? NO!

Cost a few bucks to get Roz involved, but considering the time she saved me, it was definitely worth it.