Unless you have direct control over the shipping condition/method/means, certain things (CPU heat sink, GPU card) are not securely mounted to the solid case and can break loose or simpley break off given a sharp/violent enough impact. Once, driving with my case in the trunk lyeing on its board side down, I had RAM come loose and then the PC didn't boot until I pulled out and put it back in properly (it's probabley safer to transport plugged into your board, but give it a good look over when unpacking and setting up).