[makkonen]

You shouldn't even need to kill data.img if you're just changing the zImage/modules. If you want to be extra safe, you can. (And if you're upgrading to a new system.sqsh, you probably should.)

And sometimes the data.img does get corrupted somehow (don't know why), and needs to be rebuilt... but you lose all your Android settings when you do that, so no sense in bothering unless you're having problems.