2" to 3" exhaust... Worth it?

Brookes, David spoke about the use of large empty box or a center in, center out flowmaster type of box right at the end of the headers to enable the exhaust gas/pulses to rapidly expand into it and drop the pressure, sort of like it does at the end of the tailpipes.

I think this is sort of simplistic way to describe what he meant by a " large pressure cancellation box".