There are a lot benefits of doing cardiovascular training. You're basically going to strengthen your heart. You'll find that your resting heart rate might decrease. Which is just a sign that your heart is literally becoming more efficient at doing its job. You will also see better body composition. Meaning less fat and more lean tissue. And the more lean tissue, the more muscle tissue you have, the more calories you burn at rest. You're going to get better endurance, better stamina. Just being able to go up a flight of stairs without getting out of breath. All of these things are going to happen through cardiovascular training.
Whether you choose running, cycling, swimming, rowing, or even some forms of weight training can be cardiovascular. As long as your heart rate is getting elevated and staying elevated for a period of time, you're going to reap the benefits of cardiovascular training.
There's a big misconception on how cardiovascular training should be done. Should it be done at a low intensity or should it be done at a higher intensity? People tend to do exercises at a lower intensity because there's a myth that doing lower intensity workouts will burn more fat. And to some degree that's true, because your body does more fat when you are at rest. It actually burns the most fat when you're sleeping. So that's not to say you want to sleep to burn fat. You actually want to just burn calories. What's the type of exercise you could do to burn the most calories? It's not going to be doing low, intensive exercises like walking on a treadmill. It's going to be doing those higher intensity type exercises.
So unless you have a reason you can't run, you can't row, you can't do aggressive cycling, then and only then do you want to err on the side of doing those low intensity exercises. And you would also need to do those lower intensity exercises for a longer period of time to get the same benefit that you would doing a higher intensity exercise. That potentially could be shorter, and just therefore shortening up your time at the gym.