I guess the benefit is to condition your body to make the most of the energy reserves it has rather than relying on topping that up with food. In my experience the conditioning it takes to do that isn't worth the effort, so I'll eat if I'm out for more than 90mins or so, though might go longer if it's easy and shorter if it's a harder effort where I'm bothered about performance.
There's also a personal element to it. I'm pretty light and my body doesn't naturally carry much in the way of reserves, so I've accepted that I run better for longer if I eat. Also, my preference is for longer/ultra stuff, so getting good at fueling on the move is a necessary skill. If I were focusing on say HMs or medium fell races, I might think differently.