Update: Looking back at this I've made it sound like a cure-all, which it isn't - perhaps I've been a tad flippant. But hey, the beauty of the blog is that I can pop back in and fiddle about a bit more, so here goes:
This has worked for me many times, when I'm working on a simple, usually asymmetric* layout. Bold text, simple graphics. Very much in the Constructivist or Swiss styles, or epitomised by the likes of Matter, Zwart, Muller-Brockman. The angle has a tendency to suggest movement, upward in this case, while the horizontal can feel too stable when drama/dynamism is required. Think Suprematist paintings like this more specifically stuff like this or this. Or this.
Is that any better?
* Actually, I really only ever do asymmetric, but that's another story.