Ratcheting up the pressure.
Metering "shock and awe" out over time might have an effect like twisting someone's arm more and more- threatening to break it. It also allows for more BDA.
Spreading the attack out also allows time for the Iraqis to provide first aid, take wounded to hospitals and put out fires . It also gives people time to change their minds and leave the city. This is consistent with our stated objectives
I hope we continue this approach as long as possible.