People may have vitamin deficiencies and there are situations where an extra boost may be recommended.
Breastfed babies: Vitamin D and iron
Tween and teens years: Vitamin D and calcium
In your 20s and 30s: Folic acid, iron and B12
In your 40s and 50s: Omega-3 fatty acids
Your 60s+: Vitamin B12 and multivitamins