It depends on what your goals are. If you are training for athletics (football, baseball, hockey, soccer, whatever) then you will need cardio training.

HIIT works best for most sports because it's the most realistic. Example: a play in a football game is 5-10 seconds of operating at 100% followed by 30 seconds-1 minute of rest. In addition, there is also research that suggests HIIT will help you burn the most calories over an extended period of time (it helps you burn more calories while at rest is the summary).

The physique you obtain from body building will do you no good if you can not bring it to bear for more than a short period.

Like the other guys said, if you're trying to bulk, cardio is counter productive; you're better off adding another set to your workouts. If you are trying to cut and operating at a caloric deficit, then cardio will help you achieve that goal.