Most of it is just personal experience and preference. Once I got started monitoring my food intake (which actually happened about a year before I started lifting, when I was just doing bodyweight exercises and running), I never wanted to go back to worrying about "what's in food X" or "does this have too many/few calories?" Now that I'm consistently training, I could probably get away with loosening up my diet on occasion from a body comp perpective, but I just don't see any reason not to try to optimize what I'm doing, whether in training or eating. Also, I've read enough on physiology and nutrition that, frankly, I wouldn't enjoy eating something with, e.g., a bunch of trans fat anymore.
If anything, in my experience monitoring caloric intake has been invaluable for consistently gaining weight, so I'm always slightly irritated when clean eating is equated with undereating. The problem comes when, a la jkurz, people attach outside significance to numbers and become paranoid because "4500 calories is so much, there's no way my body needs that," even when the scale's lack of movement says otherwise.
In terms of nutrient partitioning, I'm really not very far from your/BiggT's position: what you do in the gym and other athletic activities (e.g., sprinting as HIIT or for a sport) are by far the biggest determinants of where the food you eat goes. The main advantage of "clean" eating or at least some attempt at nutrient timing for partitioning is, IMO, insulin management. So as long as you're spreading your calories out over the day and avoiding sugary/processed carbs, especially when insulin sensitivity is lowest, most other attempts at "cleaning up" a diet probably don't make much of a difference in body comp.