Cardio is often paired with getting in shape and dropping that unwanted body fat but is it necessary?
Let me start by saying I believe everyone who is serious about health and fitness should be doing some form of aerobic training to keep the heart healthy. Although, to lose weight/body fat there is one major factor that needs to be taken care of and that is you need to be in a calorie deficit/negative energy balance, meaning you are expending more energy than your body is taking in daily over an extended period of time.
Say for example I have a client who maintains their body weight eating 2,500 calories per day and lifting weights 5 x per week. For this client to lose weight they will need to to put themselves into a calorie deficit/negative energy balance by either reducing their calorie intake (I recommend 300-500 calories below maintenance) or expending more energy from training (cardio/weights).
The way this client puts themselves into a calorie deficit/negative energy balance is completely up to them. In most cases I would suggest adding a small amount of cardio (example: 10 x 20 seconds sprints 1 x per week) and leave it at that until fat loss progress stalls. From here you just repeat the process. In saying this, some people would rather keep their cardio to a minimum or even none at all and simple eat less food. Either way you choose to approach it will give you the same results!
Cardio should be used as a tool to put yourself further into a negative energy balance, it is NOT necessary for fat loss although as mentioned above it should be a priority to keep aerobic training as part of your program to keep your heart healthy.
(500 calories burnt from lifting weights is no different to 500 calories burnt by doing cardio OR simply eating 500 calories less.)