Actually what it does is to force a boot to bank0 of the XCHIP.
This is convenient if you have your chip booting default to another bank.. like if you put Evox M8 in Bank5 and set it to boot default.
Only way to get back into the XCHIP setup menu is by pushing the button during boot.
Furthermore, if you use the Evox BIOS you can make an EEPROM recovery by holding down the button for about 5-10seconds during boot.