For years I've been interested in knowing how many total pounds were lifted during a session. So I kept track yesterday, and lifted a total of 13,100 pounds. Thought it was interesting. ;D
I think that's another variable that you can use to keep "improving" or making progress throughout your training. Lets say you've maxed out weight and reps on most of your exercises.... Well if you did two extra sets than what you normally did then you progressed. You were able to lift more volume that day instead of more weight, more reps etc etc. A lot of pro bodybuilders track lifting this way too.