Prioritizing Training Goals
The short answer is: it depends.
Training is a balancing act between many different variables that interplay with each other to create an end result. The end result should goal specific and related to one or two attributes of health and fitness. For example, you may devote a training program with a goal of getting stronger and getting leaner.
The more similarities the goals are for the training program, the more likely they will both be achieved. It would be foolish to expect the same program to increase your 1 rep-max deadlift by 15% and to improve your time in a half-marathon. Although both goals can eventually be achieved long-term, one goal would have to take precedence over the other to not detract from the first goal. Welcome to periodization!
Periodization is an organized approach to planning different phases of training. This is important in athletics and for those that have widespread goals or a “fitness bucket-list” with multiple events that require specific focus.
When you are serious about getting bigger or stronger, cardio will usually take the back-seat. It is still important that cardio gets done in this stage of training (for health and performance reasons) but it should be restricted in duration and frequency. Programming the strength portion of a training program requires tactfulness in trying to achieve an optimal stimulus while managing recovery to achieve the greatest training effect. After the strength training plan has been established, cardio can then be considered.
Because cardio training is catabolic (muscle-wasting) by nature, it should be programmed in a sense that it does not interfere with the anabolic (muscle-building) goals of the program. I find it most fitting to incorporate some lower intensity cardio training during my non-strength training days. If I do any cardio on the same day as a strength workout, I will plan my day so that there will be two training sessions (strength and cardio), separated by at least a meal.
Another approach is the high-intensity interval training (HIT) for cardio. This is a great approach as the HIT training is more effective at preserving muscle than traditional cardio, if done in short durations and with high enough intensity. The downside to using HIT is that it is harder to recover from and it can also interfere with strength training. If you are following an intense strength program (squatting and deadlifting above 80% of 1 rep-max regularly), high intensity methods such as sprinting might leave you more at risk for a hamstring or hip flexor strain.
If you are more concerned with keeping a lean physique and a healthy heart while trying to get bigger and stronger, realize that you might have to sacrifice some gains in your size and strength as you take more of a balanced approach to training strength and cardio. This might consist of a higher frequency of cardio or a combination of circuit training, HIT, or anything else that gets your heart rate elevated for an extended period of time.
To summarize, the main thing to consider when planning your training is your goals and effectively prioritizing them. If you want to focus on improving your strength or lean mass, it may benefit you to limit the amount and type of cardio that you do for the time being. Once you have achieved your strength or size goal, then you can re-evaluate your training priorities and give cardio a higher priority if you would like.