With all this talk of how much you lift and all that, it all comes down to what your want to do with your workout.
If you want to build muscle mass and get huge, do higher weights (within reason). The higher the weight the more your muscles are exerted and the more they regenerate and grow, giving you larger muscles.
If you want leaner muscles and to get ripped, use higher reps of lower weights, thats how you get cut and your muscle definition is greater but the mass isn't as much.
To each his own, but once you get to a mass you are happy with, I always suggest to transition to lower weights at higher reps to sustain your mass, while also putting your muscles through a good amount of work while not over exerting them as much compared to high weight and normal reps.
That's not entirely true. You could lift heavy all the time, but if you don't take in more calories than you burn, you won't gain mass. And for getting lean, you could lift high reps with lower weights, but if you eat McDonalds for every meal, you aren't going to get lean. It all comes down to nutrition when you are building muscle mass or losing fat.