Chris will probably agree here:
Oftentimes, your food sources are much worse than you may think (or perhaps you know it, but are having a hard time fixing it). Usually, this means fasting is less effective and you'll, in general, feel worse when fasted. I've personally been in both situations (great dietary choices, and let myself fall of the wagon) and fasted&worked out while fasted. I can say with a certain confidence that while on a diet consisting of great food sources, fasting felt GREAT and I'd prefer to remain fasted for the higher energy level (still in a sympathetic nervous system state).
However, for whatever reason, when my diet was terrible, fasting just felt either 1) Not much difference/not worth the hunger resistance, 2) worse than if I had eaten crap.
**I should note here that I'm mainly talking about a fasted state in the morning/out of sleep, via not eating breakfast, held until at least lunch time**
And to reiterate Chris, Post-work out nutrition is much more important.