I believe @Than_Bogan s thought that the swing set comparison doesn't really apply because the boat is moving forward makes it different is sound.
I see it as almost a race forward in the course between skier COM and the boat in relation to the slalom buoy.
Our advantage over a swing set is that we can get as wide as possible and as much as necessary, to be able to build speed, angle and thus momentum on 1 ball. Our original in-turn (cross-cut) for 1 ball builds speed and momentum right thru the arc behind the boat and depending on body position, past center line to course width if so chosen. While not ideal due to timing and over speed problems, we can continue to have, (let's say preserve) speed and momentum past the centreline.
(Seth Stisher's ipad explanation in YouTube shows this beautifully)
With a great and appropriate amount of speed and momentum built coming into clean, (not white water or boat spray) water surface, keeping the handle in tight and elbow at hips does a couple of things:
1) I think it keeps the line tension or connection at COM. This in fact keeps us in balance while maintaining desired ski angle at desired locations course-wise. Poorly said, but let's just say that in the absence of line tension from a decent out-bound trajectory and elbow to hip connection pre-buoy, you have slight, or no line tension which for me can result in slack line, an off balance turn and edge change which produces and over or under load ski angle and body position coming out of the turn.
2) I also believe that having that line tension and elbow to hip connection pre-buoy delays, or should I say maintains speed and out-bound momentum (inertia?) to a point that allows skier to get wide and high enough on the boat to reach the ball in control.
I learned a long time ago from Andy that as soon as your handle has moved away from your body, you have effectively committed to the turn. This results in a flat ski, slowing of speed and lost of momentum, too early a reach and stalled ski, broken waist, OTF fall, bad attitude and diminished confidence, but I digress.
One of the biggest things I realized as a benefit of the pre-ball yank or line tension has given me is the connection to the boat which really really helps balance and setting of ski angle during the critical edge change time. When I lay off early, stop cutting, lose stacked position too soon, stand up and glide in the white water, my ski is flat for too long, the buoy seems narrow and my trajectory x-course is lost.
This whole point was reinforced by KC last October in FL when we spent a full morning working on timing and intensity of the outbound cut, turn and cross cut trajectory for just 1ball.
Both coaches encouraged us to get wide, build line pressure in stacked position and keep edging wider (at least for me and the 2 Pierre's) enroute to 1 ball And to keep the handle I until last second where the reach will allow less tension on the line, body and ski then move forward and come around appropriately to set the new edge and x-course angle. With a good reach at the right time your body is also setup to be able to take the hit from the boat after the buoy.
Trying to do this without wide® course line tension is I believe much more difficult.