Being a powerlifter, I'm sure everyone can guess what my opinion on cardio is However, general physical preparedness (GPP for short) is very important, and it is a big factor in how your body reacts to volume and intensity of training. Louie Simmons has stated that raising an athlete's GPP pretty much universally results in raising overall athletic performance regardless of the sport, however westsiders are not fans of things like running, cycling, or other traditional "cardio" workouts, because they don't carry over benefits to strength training very well.
Instead, the westside method encourages extra workouts. These extra workouts are done with a very high volume and very light load, with basically no rest between sets. Supersetting of exercises for alternating bodyparts is common, and weak points are focused on in exercise selection. The entire workout should last between 15-30 minutes.
As an example, I recently started doing one extra workout a week for conditioning purposes, which is basically comprised of a bar weighing 135lbs, which I proceed to squat, deadlift and power clean at a brisk pace until I am very short of breath, at which point I do some swiss ball curls for ~30 reps then go back to doing the squats, deadlifts and power cleans - this is repeated for 25-30 minutes. The difference this has made in my conditioning already is impressive, and I suggest to anyone who hates doing cardio to give WSB style extra workouts a try.