Depends on your goals. If you're a bodybuilder then lifting is the priority. Again most bodybuilders use cardio for cosmetic purposes and not athletic. Most walk fast on an incline. If you are training heavy and looking to increase athletic function then doing cardio on non lifting days works well.
This is what I do. I don't expect anyone to do what I do. Just saying what I do. I lift three days a week and try for three cardio days on non lifting days. I use a three way split with low sets training a set to positive failure. Day one is back and chest. Second day is legs. The last is delt and arms. Do the body parts only get hit one time? No there is a ton of over lap and the body fatigues as a unit and not localized to the body part trained. Speaking of over lap every pulling motion in back training is hitting the bicep hard. Every pushing on chest day is hitting tricep. So arms are getting hit twice a week. On back day it's either included deads or power cleans. Legs are getting hit twice a week. On directly on leg day and once on back day. I could go on.
