In developed countries, where such a variety of food is avaible, it is hard to see why anyone should lack nutrients. But surveys show that a substantial proportion of people are on or under the borderline of safety, mainly because they eat badly balanced diets.
A less active lifestyle means less food is needed, making it more difficult to obtain all the necessary nutrients, especially, if people consume substantial amounts of sugary foods and alcohol, which supply almost no vitamins or minerals. The fewer calories eaten, the more important it is that almost every calorie carries with it some vitamins and minerals.
Some people have a higher than average need for one or more nutrients. More of a vitamin or mineral is not automatically better, but we now know that for some vitamins, a higher intake can benefit people who show no sign of being deficient. For many vitamins, we can aim for optimum levels.