Well, once you reach your requirement for fats in the diet, there is really no reason to eat more. Sure, there are certainly benefits to increasing omega-3s, but you don't want to go overboard. The goal is to eat as much as you can without getting fat. Fat is stored much easier than carbs so you can be a little more loose with carb intake if your fats are under control. (I don't want to hear arguments that "calories are calories"...you all know what I'm trying to say here)
So, I guess what I'm trying to say is that there is no other reason than the ones you are already familiar with. Fat is more calorie dense thus you get less food if more of it is fat.