This is not my opinion, it is stated to keep everyone safe. You should be lifting as fresh as possible. This is extremely important especially to anyone who lifts heavy.
people say doing cardio before workouts gets your blood pumping thru your body better ...
i tried doing it, but i saw no benefit to it. I prefer starting with the weights right off the bat, as i have more energy ... and for the bloodflow ... doing a quick set of light weight gets it going.
some times on leg day, I'll cycle for 5 mins just to warm up my joints, but really not enough to qualify as cardio.
I like a short, slow, steep incline treadmill after my leg workout to help stretch the muscles back out before my drive home.