The answer is quite simple. In cardio training you train the heart muscle and the lungs so that the different organs will also function better since more oxygen gets to the cells in someone with a healthy condition, In strength training you train the other muscles of your body. Cardio training will therefore improve your condition and make your general metabolism work more actively. The better your condition, the more efficiently you can do strength training. We always advise to do a combination of both. Even after a heavy strength training, it is useful to train light cardio on the bike for another 15 minutes to process the formed lactic acid.
Cardio training will also increase your muscle strength if you train against heavier resistance. Higher resistance also means higher heart rate and then you have to keep this in control for optimal results.
A handy tip for the deep-sea divers. A person who does cardio training 3 times a week will do a lot longer with a bottle of compressed air than someone who does not exercise.