well, cardio isn't just to burn more calories or lose fat...
steady state cardio (not HIIT) increases the size of the ventricular chamber, which means your heart can pump more blood with each stroke. this also lowers your heart rate.
lifting and HIIT increase the strength/thickness of your heart, which allows it to contract with more force. steroids (and high blood pressure and other things) also increase the thickness of the heart, which means doing cardio on cycle is a pretty good idea, from a longevity standpoint.
i'm not talking about marathon training, but 20+ minutes a couple times a week shouldn't throw off your gains much, especially if you're on cycle.