Hi Woody,
Jib trim and counterbalancing are two different things.
The jib swivel location on the boom is a fulcrum point but not to perfect a balance so lead in added within the boom to reach a point close to neutrality so the jib will swing very easily side to side. Hence, when you turn downwind and the jib beomes unloaded, the slightest air movement will cause the jib to swing out and be held by that air. The wing on wing effect becomes so more easily through counterbalancing and is quite effective in light air.
The use of jib trim is a functional part of tuning while underway through the use of the sheet line. To weather, the balance of the sail plan can be altered to allow the boat to head up more into the wind, can alter the slot in changing air pressures and allow you to pinch, for just a short while, when needed. On the run it can allow dumping pressure on the jib in a gust but mainly to trim in the jib for more a efficent use when wing on wing.
The use of jib trim does increase power consumption with an extra servo and with larger torque values to hold the jib sheet at the arm right angles to the fairlead. This power need has not been a problem except in the wiring of the on board gear. (Read Phantom of the Bilge)
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