Is there any advantage to use the 'leader line' ? Less wear on the LE/TE ? Less wear on the flying lines ?
Exactly and a couple of other benifits I've heard.
Some people feel the heavier line falls out of the way quicker giving less chance of tip wraps.
Some of us vision impaired folks find the heavier and bright colored line easier to see at a distance for unwrapping those tip wraps that didn't happen because we had the heavier line
no really it's much easier to see what your lines are doing near the kite at a distance