Doesn’t the Empire take a huge economic loss from the lost productivity of an entire planet? They were presumably paying taxes and providing resources to the rest of the Empire. Presumably the loss of that planet’s output would have to be made up by increased output from other planets that were either slacking in productivity due to rebellion or threatening to rebel and withdraw from the Empire altogether. It doesn’t seem to make good economic sense.
The Death Star is pretty badass until you pause to reflect on its practical and economic implications (via John Gruber):