It doubles the gauge of the wire, which can have some benefit. Other benefits are more controversial. Some theories claim that the wires each carry separate frequency ranges due to the capacitance and inductance of the crossover parts. Whether it’s audible is a variable, as each system and situation is unique. It’s always best to give it a try and see what you think on your system.

Bi-Wiring and Bi-Amping Explained see here!

Mike

I think the biggest benefit of bi-wiring is the heavier gauge, but all else being equal in gauge if I can get a better quality cable with an internally bi-wired cable for the same price as a lower quality externally bi-wired cable I’d definitely go for the former.

Not completely sure what you mean by separate verses internal.  If you mean that the cables are separated by a distance of several inches then it would be to reduce coupling from the signal in one cable pair into the other cable pair.  I think b-wiring is most beneficial when the speaker has two pairs of terminals, one pair for the upper frequencies and one pair for the lower frequencies.  In this case, the current flowing through the cable dedicated to the low frequency speaker terminals will create an electric field around the cable but due to the seperation, it will not couple (or couple to a lesser degree) into the cable dedicated to the high frequencies.  There was good article on this topic, I think from the Vandersteen speaker company.  I just biwired and felt like there was an improvement, but so hard to tell plus it could be an amp breaking in.