The benefit of doubt provision means that, in weighing all of the evidence presented for a disability claim, if the evidence for favourable or unfavourable decision is equal, then the benefit of doubt goes to the veteran. So it's very much an adjudicative process that looks at all of the evidence, weighs it, and applies the benefit of doubt when it's not entirely clear one way or another.
On December 3rd, 2013. See this statement in context.