I don't think cardio is a necessity when trying to reduce body fat, more notably at higher %, when this can be achieved majorly by controlling your diet in combination with resistance exercise. As you reduce your bodyfat % and are trying to reduce those final stores I believe cardio becomes more important, especially in a morning during a semi-fasted state (following ingestion of BCAA's), but again nothing particularly testing or stressing on the CNS as this will already be depleted from the reduced caloric intake.
However, this does not mean to say that cardio isn't important for overall health benefits and it should be employed, perhaps even during bulking cycles, to maintain your conditioning. Again, just don't overdo it and adjust the calories accordingly.