I don't know why I'd pull only one trash pack if we can handle two or three. I don't know why you'd advocate for that either so long as no one's dying. There's nothing interesting about trash. Just pulling more of it makes life more interesting for the tank and healer. As a DPS, you should be AoEing after a certain number of mobs anyway. I guess I don't see what's better about fighting one pack at once if you can comfortably fight more than one.