By common I mean it's something that your average General practitioner doctor will encounter. Pregnant and Nursing mothers are often told to take supplements with good reason. Also of note absorption issues are just as important as diet which is one of the reason B12 shots for example are used to treat deficiency.

With that said, taking a daily multivitamin is often overkill taking it weekly is often just as useful. It's just that they are cheap enough that trying to figure out the ideal dose is generally a waste of time.

"By common I mean it's something that your average General practitioner doctor will encounter"

Well, sure, but that's during specific cases where the person knows that there's something wrong with them. It's not commonly "accidentally" discovered during the course of your regular physicals.