Intravenous therapy is a dynamic way to administer medicine (vitamins, minerals and other important healing substances). There are many circumstances where substances delivered intravenously act more powerfully than taking them by mouth.
Vitamin C is a great example. It's estimated that taking Vitamin C orally results in less than 20% being absorbed in the blood stream. On the other hand, administering it IV results in 100% absorption.
Another important advantage of IV administration is volume. IV administration of minerals and vitamins can be infused in far greater quantities than possible orally. This effectively changes their function.
Administering Magnesium IV can be given in much greater quantities than is practical to give orally. This allows for much greater potency. In addition, the familiar magnesium diarrhea is avoided completely.
Finally, IV administration rapidly puts healing substances right where they are needed most; the cell. It is our cells that need these nutrients/substances most desperately for healing.