There is no real definitive answer to this question; it depends largely on the types of vitamins being consumed and by whom.
If you are a naturally healthy person, with a balanced and varied diet, you are likely to be getting all the vitamins and minerals you need from your food. Any additional vitamins you take in the form of supplements is likely to be excreted from the body through your urine – bypassing the body completely!
If you however, are someone who does not have a healthy diet, and tend not to eat your recommended portions of fruit and veg each day, then a good multi-vitamin is likely to be a good idea for you. Helping to replace the lost nutrients which can help keep you healthy.
Other supplements commonly taken include fish oil, which is good for the heart and bones, and specialised vitamins for specific conditions like garcinia cambogia for weight loss. The jury is generally out about whether these are effective or not, as many studies have come back inconclusive.