ATP Science have specifically formulated Z-MAG, to provide essential minerals for some very important metabolic processes such as:
Promotes energy levels
Decreases muscle pain, muscle tension and muscle stiffness
Supports a healthy cardiovascular system function
Getting essential nutrients in our diets are becoming harder and harder.  The typical Western diet is very low in vegetables which is where most minerals are found, and those who are eating more vegetables than the average person generally do not consume organically grown vegetables but more hydroponically grown vegetables typically found in supermarkets.
Sure, there are many pros in hydroponically grown vegetables such as that it saves you space, water, having to weed the garden, and fewer pests and disease.  But you miss out on the soil organisms that sit on the roots of soil-grown organic vegetables that are essential for other aspects of health.
Consider that if you are an athlete, exercising more than the average person, or just generally busier than most people, that you are likely to be using a lot more essential nutrients than the average couch potato.
Especially minerals.
Minerals are obtained mainly from plant sources, especially organic plant sources.  Deficiencies in minerals are becoming more prevalent in Western diets and have been associated with many common disorders and disease symptoms.  Many processing techniques employed today in modern food preparation deplete foods of vital nutrients which include minerals and is one of the main reasons processed foods have to be fortified with minerals.  Zinc is one of the most dominant minerals used in the fortification of foods these days due to it being deficient in most processed foods.