Do you get the right amount of vitamins? If you have a very balanced and healthy diet the likelihood is you get all or most of the vitamins and minerals you need to sustain normally bodily functions however most people rarely have a balanced and nutritious diet, or they eat infrequently, no set meal times etc and therefore what you eat is never planned very well. It's important your body gets regular vitamins to sustain everyday bodily functions and if your diet is not up to scratch then starting with multivitamins will be like taking out a insurance policy, you're not sure if your are going to need it but, it's best to be safe.
The multivitamins you choose to purchase will depend on your lifestyle and activity levels, and what else you need in your diet, basic multivitamins will have 100% RDA (recommended Daily Allowance) of most of the major vitamins. This is suitable for most people and there are plenty of variations such as multivitamins & minerals, multivitamins and calcium, etc etc.
If you train regularly and want to ensure your body has the best chance of repair and you are not hindering it's normal functions then a super multivitamins will ensure everything is topped up no matter how hard you train, these normally come in the thousands of percent of RDA and therefore much over what you really need. No need to worry to much as water soluble vitamins will be passed out of the body in urine (this can sometime make your urine go a very neon yellow color)
Don't leave it to chance, top up with multivitamins