Importance of running for a pitcher

My son (16 yrs old) is in the phase 3 of tuff cuff. He is doing very good with the weight lifting: however, he does not feel the running portion is important. What benefits do the running(both sprinting and long distance) give pitchers. He also long tosses every 3rd day.

conditioning to build up endurance, makes you a better athlete in general, and long distance running takes the lactic acid out of your arm to help prevent to much soreness