The reason for cardio after a workout is, for the fat you want to save your strength to workout.
If you workout first your strength will be better with the weight.
Also after you burn all your carbs from the work out, then hit the cardio you will use your stored fat as energy. You need to have a higher protein intake with some protein shakes to hold on to muscle with cardio after a work out, so you don't use muscle mass as fuel (breakdown of protein in the muscle).