Years ago, at a garage sale, I stumbled on a copy of Swain's other book, Techniques Of The Selling Writer. Took it home, looked at it and decided it was beneath me -- or at least below the level I fancied I was writing at. A few years later, after three more novel rejections, I took it out and read it. Really read it. It's a basic book, I won't say it isn't. But it covered so much stuff I'd somehow missed. Like the creation of story scenes. When it had sometime to settle in my psyche I started selling short stories. Shortly after, I sold novels. I have now sold eight books -- some not under my own name -- and can live from my writing.
As for this book -- I never had a need for a character book. It's one of the things I do intuitively. However, when my husband was struggling with characters I thought "Well, Swain helped me, so..." and I bought him this book. He studied it and his next story was published.
I can't garantee these results -- there's so much to the selling of a story or novel that does NOT depend on technique of any sort -- but I can tell you that when I'm mentoring someone -- which I've done a lot since then -- and their issue seems to be technique, Swain's books usually cure the problem.