IMO, the benefit is very small, and even has some disadvantages. Actually, for 99% of amps, it's just a disadvantage... And a waste of parts. If I'm not mistaken, GR Research is really into wiring and botique cross overs. Things not so popular around here.
But to better answer your question, it makes the impedance profile more flat, thus making the load easier for the amplifier to drive. At least that's the argument. In reality, my feeling would be it's better to keep the impedance higher, so the amplifier doesn't have to provide as much power. It's a really small difference either way.