Bi-wire Clarification

One of my friends (who posts regularly here) and I have been swapping emails over and over talking about bi-wiring. I think we are getting the general idea after emailing different cable companies, but what I want to know is how it makes a difference (1) and (2) how do external and internal bi-wiring differ.

I'm looking for technical as well as non technical information here. I know there have been many posts on biwiring, but in looking through those, I haven't found my answer. Also, how many people use the idea that a smaller cable should be run to the tweeter and a larger cable should be run to the woofer. (assuming a 2-way set up)

Thanks for all your help.

Seth