Fasted Cardio is only more beneficial due to timing and not actually being fasted... Has been proven over and over. The benefit of fasted cardio is that it is done first thing in the morning. The sooner in the day you boost your metabolism the longer it stays boosted, the more overall calories you burn throughout the day. That's the benefit guys... that's it. As a matter of fact it has been shown to increase the amount of calories burned during cardio if you have 20-30 grams of protein before doing so...
Just notice how 81dcs said he had been doing fasted cardio for 2.5 months, it wasn't actually fasted, and by taking aminos it actually shortcuts the digestion process and sends in aminos into the blood stream that can be immediately broken down into ATP and used for energy by the muscle tissue. He said he has been getting great results, that is because it is the early morning cardio, and not being fasted that is increasing the total caloric burn for the day.
If you do cardio in the morning your metabolism increases and stays elevated for hours and hours, but if you do our cardio at say 6PM your metabolism stays elevated for a couple hours then your circadian rhythms kick in that slow the metabolism down and prepare you for rest. So the later in the day the cardio is done the less time your metabolism spends in the increased rate as the circadian rhythm trumps the metabolic increase from the cardio.
Now nothing negative is going to come from doing fasted cardio unless you have blood sugar issues and go hypo. However there is also no reason to try and make sure you have not had any food before doing morning cardio. I would recommend that if you want to keep blood sugar lower during this time to only have protein or fat prior to the cardio, but even if you have carbs they won't really begin to elevate your blood sugar for about 15 minutes after ingestion if fast acting.