[Mobhack]

It is not "cheating" - It is a technique used by artillery in real life, called the "silent barrage". In real life the battery lays onto various predicted points ready to fire on them, but they wait for the forward observer to actually call for the fires to start (in WW2 by radio, in WW1 a rocket or flare).

Useful for a quiet attack onto a position where you think the enemy may well be, but not calling for the artillery fire to start until an actual enemy is found near one of the preplotted targets. Thus the fact of the assault happening is kept quiet for a few minutess or more until the troops actually bump the defenders.