The gears are manufactured to better tolerances. This means they make a lot less noise. A cheap movement can be heard across the room, a Seiko is silent.
Because the parts fit better, there is less friction. Less of a load on the motor means the battery lasts much longer in a Seiko.
Because the parts fit better, there is less friction. Less of a load on the motor means the battery lasts much longer in a Seiko.
They also keep time better.