Whatever their goal people seem to do far too much cardio, even if they are a runner. Part of this is the common misconception that cardio is best for burning fat; it is not as any, and all, exercise will burn fat.
If you look at simply increasing health and reducing markers for heart disease any exercise is better than no exercise and carrying out any regular exercise 2-3 times a week is enough on its own. You don’t have to do any specific cardio at all as your heart and lungs will be working as you lift weights if that is your chosen method of exercise.
If you are trying to lose weight/fat you have to consider that, as you get fitter you will burn less calories for the same exercise/distance/intensity. That is kind of what getting fitter is all about, doing more for less. So therefore, to keep burning calories you have to regularly increase the distance and/or speed/or intensity. The problem is that there are only so many hours in the day so do you really want to keep increasing how long you spend on the treadmill/bike/stepper? Increasing intensity can lead to injuries and some people just aren’t built to run fast or for impact. How fast can you go?
Also, cardio inevitably reduces muscle as the body tries to decrease the amount of weight it has to lug around and source energy for. Less muscle equals a lower metabolism equals less calories burnt. So cardio can be a vicious circle.
If cardio is your thing then mix and match it up; running, cycling, rowing, cross training, spin, circuits and so on but lift some weights too.