So, this morning, I turned the tables. I focused only on him (in the brainstorming process), and saw the entire plot from his perspective only. And when I did that, it opened up everything. I understood his motives, saw why he would react in ways he did. And I started seeing my female protagonist through his eyes. The story suddenly feels richer, brighter, stronger. Even though, in the story, I haven't changed the POV at all (it's still "her" story).
This situation reminds me very much of the not-published "sequel" to Twilight, called Midnight Sun (okay, all you Twilight-haters, bear with me a second, here...this post has less to do with Twilight and more to do with POV). ;-)
I read Twilight years ago, at the suggestion of a Creative Writing student. I thought the writing could've been stronger, but I liked it. I thought the concept was creative. But I hated Edward. Hated him. I did not understand why the world had fallen in love with him. I saw him only as manipulative, controlling, and even a bit misogynistic. But Twilight was all from Bella's perspective, never Edward's. Thus, we only saw him through her eyes. There were whole periods of the book where we didn't "see" Edward at all (because Bella wasn't in his presence). Therefore, much of his jerky behavior was a mystery to the reader.
Well, somebody told me to go forth and read Midnight Sun -- link here. It's a novel told from Edward's perspective. It's still the Twilight story (nothing changed, plot-wise, from that book), but it totally switches to Edward's POV. While reading his side of the story, his perspective, a strange thing happened. I started to like him. I could empathize with him. I finally understood why he did the things he did in Twilight. It all made perfect sense.
And though I don't plan to write a separate novel from my male character's point of view, it's still imperative that I know who he is, why he makes the decisions he makes, and what he's thinking when my female protagonist has a scene with him.
In the end, I think it's essential that we writers know every angle of the story we're telling, and that even includes the perspective of characters whose POV we're not highlighting. The story will be stronger and richer for it.