For me, the main purpose of revision lies in the word itself: re-vision. Revision is not just about refining what's on the page, it's the process is about making the choices I've made during the writing phase more conscious and deliberate.
Racism is a major issue in my novel, and I've revealed the race of all my characters equally (meaning, among other things, I describe skin tone for all of them, and do not let the reader default anyone to white; if a character is white, I say it, the same with my characters who are black, Native American, Latino, etc). There's only one character I've left deliberately ambiguous because I think most readers, in the absence of a physical description, will default him to white despite the way he's been described and the way he acts. And I want the reader to have a moment of awareness, when I reveal his ethnicity, about that assumption. The scene I'm working on should make his ethnicity much clearer, but it's also a reminder to me about the purpose revision has in bringing the unconscious choices I made while writing into a purposeful, conscious decision that serves the story.
I see this a lot in my clients' work -- aspects of the novel the writer hasn't fully realized because they haven't interrogated and questioned their intention in putting it on the page and how it serves the story, as well as evaluating whether they've achieved their goal. Revision is the process of making all of this a conscious choice.
And now, coffee break is over, back to the novel.