> Question: What's the benefit of shorter lines?
Greater maneuverability (kite AND board), & if all else is equal*, better
upwind (less line drag yields a better Lift-to-Drag ratio). The kite
maneuverability is because shorter lines don't stretch or sag as much, so
kite response is quicker. The board maneuverability comes from the shorter
time it takes the kite to cross the window. In other words, if you suddenly
want to change your direction of travel by 180 degrees (jibe, bottom turn,
off-the-lip, etc.) there's less delay for the kite to reach the other side
to pull you in the new direction.
*if you're powered up as much, which is less likely, due to the higher low
wind limit that shorter lines give your kite.
Depending on HOW short, jumping can be better, due to the kite's turning &
speed across the window. It seems that 20 or 30m is best for jumping, but
10 & 15m for wave riding is not good for jumps.