Vitamin C is a reducing substance, an electron donor. When vitamin C donates its two high-energy electrons to scavenge free radicals, much of the resulting dehydroascorbate is re-reduced to vitamin C and therefore used repeatedly. Conventional wisdom is correct in that only small amounts of vitamin C are necessary for this function because of its repeated use.

The point missed is that the limiting part in nonenzymatic free radical scavenging is the rate at which extra high-energy electrons are provided through NADH to re-reduce the vitamin C and other free radical scavengers.

When ill, free radicals are formed at a rate faster than the high-energy electrons are made available.

Doses of vitamin C as large as 1–10 g per 24 h do only limited good. However, when ascorbate is used in massive amounts, such as 30–200+ per 24 h, these amounts directly provide the electrons necessary to quench the free radicals of almost any inflammation. Additionally, in high concentrations ascorbate reduces NAD(P)H and therefore can provide the high-energy electrons necessary to reduce the molecular oxygen used in the respiratory burst of phagocytes. In these functions, the ascorbate part is mostly wasted but the necessary high-energy electrons are provided in large amounts.
A unique function for ascorbate
https://www.sciencedirect.com/science/article/pii/030698779190080I