During Galileo firmware update, why does SDcard need to be removed and board remain plugged in?

In step 4 Galileo Getting Started - Windows Firmware update, why does SDCard need to be removed? Will the board be irreversibly damaged if power is abruptly removed? If yes, why?

WARNING - During the firmware update it is extremely important that your board remain plugged in and powered on!

NOTE: If you have a microSD card inserted, you will need to power off your Galileo, remove the card, and reboot Galileo without the card in before updating your firmware.