by going into neutral, you are forcing the transmission to grab 1st or 2nd gear again when you put it in drive, so you create just a little extra wear on at least one of the internal clutches, which I would expect to be a more significant factor than anything which happens in the motor or torque converter when the transmission is left in drive. The only exception might be a car with an underdesigned cooling system, like my '83 Toyota Celica, in which shifting to neutral at long lights or train crossings sometimes allows the motor to idle just enough faster to keep the temperature close to normal with the AC on when the temperature is above 85F.