The difference for me is that I'm not just a bber, I do endurance sports like mountaineering and hiking, so I have to be able to train my cardiovascular system differently than most guys on here. In fact, it's usually my first priority. Cardio for me isn't just to get lean, I have to excel at it.
I'm training for a tough mudder and need to be able to run 8-10 miles, and w/o enough carbs its virtually impossible.