Keeping track of how you warm up and it's effect on workout performance is a good idea ESPECIALLY if you are concerned with something like powerlifting or ME work. It's one of the bigger mistakes new powerlifters make, not knowing how to warm up for a max. Hell, CT now has entire workouts devoted to warming up the nervous system. Warming up is important. Period.
As your lifts progress, your warm ups should too. Warming up for a 405 bench is different that a 315 bench. As your weight changes, you should be adjusting the weights/sets/reps of your warmup too and the only way to actually figure out what works for you and how to progress is to keep a log INCLUDING your warm-up.
With the idea being to warm up muscle and joints, get the blood flowing, wake up the neverous system and movement pattern, all while not tiring the muscle.
Literally, one of the biggest improvements I've made recently is putting effort into figuring out how to warm up.
Now, if you are a BBer, or an ass like mr. popular here, just looking to activate the muscles and doing some 3 by 10 thing, it probably isn't as important.
It's about progression and getting all you can out of your workouts and you have to know what you have done in the past in order to progress.