Who in hell eats good healthy food all the time?
I never went back to that moron...
The RDAs of vitamins are rather arbitrary. More vitamins than some minimum are probably helpful in some sense. But sometimes lights at the end of tunnels turn out to be the headlamps of oncoming trains... perhaps surfeits of vitamins might facilitate body wear in some fashion. And none of our mortal bodies are permanent anyhow. The all things in moderation theory has a lot to be said for it.
I've read many articles about vitamins over the years. The writer of the article would ask the question about vitamin benefits to some doctor or dietician. The latter would always say if you eat a proper diet, you don't need vitamins. Not ONCE!!! in those articles did the interviewer then ask the so-called expert "but what if you don't eat the proper diet?"
Obviously then, if you're eating a lousy diet or one without the necessary vitamins, vitamin supplements help. That's why they put them in cereals after the big flap in the early '70s about cereals having little nutritional benefits.