You can't just say that without including a link :P
Anyways, I assume that the following is what you are referring to: https://www.raspberrypi.org/documentation/hardware/raspberry...
In that case, the following from the linked page might be worth making note of:
> To enable USB host boot mode, the Raspberry Pi needs to be booted from an SD card with a special option to set the USB host boot mode bit in the one-time programmable (OTP) memory. Once this bit has been set, the SD card is no longer required. Note that any change you make to the OTP is permanent and cannot be undone.
Not that it matters much to me but still something worth being aware of if you later try to repurpose your RPi for something else I think.