A friend sent me a link to this video, which is great. In it, Jim Emerson, a film writer and critic, breaks down a sequence from "The Dark Knight" and explains why he finds it confusing. It's a great primer on screen direction and the 180 degree rule, and why those things are important.
In the Cut, Part I: Shots in the Dark (Knight) from Jim Emerson on Vimeo.
When the audience is confused and disoriented, they start to use their brains to try and decipher what's going on, rather than to engage with your movie and care about what's happening onscreen. In an action sequence it's particularly important to keep your audience absolutely clear about where all the characters, vehicles and landmarks are in relation to each other. Otherwise, there's no tension or drama.