Hello,
This is for the NG; there might be differences between the classic and the NG.
The starter is supposed to automatically disconnect at 56% N2, not 46%. You would then observe the starter switch popping back to OFF/AUTO, the bleed air duct pressure flutters, and the START VALVE OPEN light goes out. If the starter does not disconnect, there is a QRH procedure for it, which essentially tells you to move the start switch yourself within 120 seconds of engaging it.
As for the FMC, you don't really gain or lose anything per se, but having the correct winds in the RTE DATA section provides you with better time and fuel predictions, which provides a bit of relief in todays world of flying around with close to min.fuel.
The FMC does use head-/tailwind in it's computation of ECON speeds, but will use actual winds in lieu of entered winds, so it will fly faster in a headwind and slower in a tailwind, even without any data entered.
Good luck.
Last edited by bfisk; 15th August 2012 at 08:09.