I'm a (soon-to-be) fitness competitor, and I switch between bulking (eat over maintenance) and cutting (eating below) and I take a powdered multivitamin when I'm cutting because I'm just not eating enough to get everything I need. If you eat a lot of healthy food I definitely don't think multivitamins are necessary but most people don't eat a varied or healthy enough diet. If you live off chicken nuggets and fries then yeah, I'd recommend a multivitamin.