Por este segmento, parece que esse comando permite que a VM acesse o USB leitores de cartões, como SD e leitores de cartão inteligente.
The following setting defines access to a USB Card Reader by the guest environment. USB card readers are typically used for accessing data on memory cards such as CompactFlash (CF), Secure Digital (SD) or MultiMediaCard (MMC).
VBoxManage modifyvm <uuid|vmname> --usbcardreader on|off
Enables/disables the USB card reader interface.