- CSC (Consumer Software Customization): It is specific to geographical region and carriers. It contains the software packages specific to that region, carrier branding and APN setting.
- PIT (Partition Information Table): You only need it if you screw up your partition table or if the firmware specifically requires it because of a change in the partition table layout.
- BL (Bootloader): As its name implies, this option is used to flash the Bootloader of the device.
- AP (Application Processor or PDA): Android.
- CP (Core Processor): We call it Modem.
If I flash all of them, i guess i should be ok. However, it might be that rolling back to an earlier boot loader blocks the ROM update (read that on a thread somewhere - boot loader 4.3 i think stops you going back to earlier BLs). If it's the same BL then i guess people would be ok.