Originally Posted by JugglerDave
...does this mean that I can either ride for 40 miles without eating anything, to the point of bonking, and burn about 1600 calories? Or I can burn 600 and eat 300 calories for net -300 calories, for about 5+ hours (75-90 miles) and have the same 1600 calorie deficit maximum?
Calorie deficit calculation is useful in determining how much recovery fuel you need. Depending on the intensity level of your effort, you can ride for hours without eating anything and not run the chance of bonking. Once you start exercising beyond about 72% of your max. heart rate, you start dipping into your glycogen stores, and taking in carbs during the ride is important to prevent the bonk.
An example: Today I did a 4.5 hour ride, burned about 3000 kcal, and took in about 900, for a deficit of 2100 kcal. It was a "tempo" ride, so I was drawing down my glycogen at a moderate rate. Once I finished the ride, I drank a recovery drink and have been snacking on carbs every hour.