why use IIFYM
 

IIFYM is a flexible dieting approach where you disregard arbitrary food labels such as “junk food” and “clean food” and focus on your total caloric intake (calories in versus calories out), your daily set macro-nutrient targets (your fats, carbs, protein), and your micro-nutrient goals (your vitamins and minerals) in order to achieve your desired body composition.

However, we should mention that IIFYM is about fitting your ‘macros’, not your ‘micros’, so it’s very much possible to achieve your desired body composition whilst disregarding your micro-nutrient intake. However for health benefits it’s generally advised that you fill your vitamins and minerals for the day.

If your lacking behind with your micro-nutrient intake, a multi-vitamin is a good stepping stone to hit those targets.

Exactly why I don't agree with it, because you lose the health benefits.
A couple of vitamins a day will not make up for the loss of eating clean.