The US has adopted in Iraq the technique of exploding a missile above the roof of a building as a way of "warning" civilians to leave the building (which is scheduled to be bombed shortly thereafter).

The problems are that (1) the people don't necessarily recognize what the explosion means, or even that it was an explosion, and (2) the actual bombardment may come so fast that people don't have time to get their children or elderly parents out of the building.

Giving this sort of warning cannot as such be bad, but if it becomes an excuse for predictably killing civilians, that is bad.