From my experiences, it's an absolutely pointless feature. It's only useful for the actual mounting of the motherboard to the case. The RAM, CPU, and heatsink you can put on the motherboard before you mount it, everything else you will need to have the tray in most likely. When all the cables are hooked up, you won't be able to move it much anyway. So it's a pretty overrated feature, unless maybe you have an extremely small case and monstrous hands (as I do), but I still had no mobility problems putting my last PC together without a removable tray.