Balloons only start to kill the 3rd line if the opponent doesn't have a gyros.
Balloons are generally only used when the opponent has run out of gyros in the battle, or when the opponent places balloons to conserve gyros and you need to conserve them as well.
Incorrect. Before the update, balloons were mostly used when the opponent sent in mortars, to break down a wall, or against steam giants Using them to conserve gyro never made sense

