spindles? lower a-arms? springs?

I know about the "scrub line" and that if you get anything like a spring bucket lower than it, and happen to have 2 flats at the same time, you could die in a fiery crash, or at the very least loose a limb or 3... but can someone explain to me why you cant run "drop" lower a-arms and drop spindles at the same time? All I can find says "bad geometry" I figured it could be something to do with wheel clearance on the lower a-arm too. I just want some one to shed some light on the subject, cause thats exactly how I was planning on static lowering my c-30.

-A.