However, I train BJJ more than the average hobbyist, and my competition classes are just 1.5 hours of hard and intense sparring, so I don't really need to.
I would personally say cardio is only important if you want to compete, or if you feel that your Judo randori is being severely held back by your cardio. It really depends on your goals. Personally, I don't train cardio on the side. However, I train BJJ more than the average hobbyist, and my competition classes are just 1.5 hours of hard and intense sparring, so I don't really need to. Before I had competition classes available to me, I had a routine to develop my cardio for competition. I used this routine because running was causing me knee pain.