Bootloader Component has a choice to select last N rows in PSoC4 uers flash excluded section of flash checksum.
This option allows you to specify the size of flash section that is intended for user needs and does not take part in Bootloadable Application checksum calculation. Other Components could use this section for storing data (for instance, BLE could store its pairing data). Default value is 0x00000000.
Refer Bootloader datasheet for more details: