Because my diet is not filled with vitamin and mineral rich foods, taking a multivitamin helps me get the right amounts of vitamins that I need daily. And because the water soluble vitamins are at 100% I can be comfortable knowing that I will not be nearing toxic levels. Another benefit with taking my vitamins daily is that the vitamins help my body produce energy.
Taking a multivitamin with the recommended dosage does not raise your intake to near-toxic levels. If you are taking a multivitamin as well as supplements on the side, then it would raise your chances of going over the recommended DV which could cause serious health problems. For instance going over the recommended DV of Iron 45mg causes liver damage and gastrointestinal upsets.
Going over the DV of vitamins and minerals can cause many health problems and can cause damage to your organs. And can damage the nervous system. Too much salt can cause high blood pressure; too much iron can cause liver damage.