No formatting is necessary, as long as the drive being used is in one of the compatible formats, see 'Compatible hard drive formats & ideal drive setup for Kwilt' to verify.
If you have ensured it is in one of these formats, Kwilt will be able to read and write to your USB storage device. Therefore you can disconnect your USB storage devices from the Kwilt device to copy content directly from another PC and connect it back to your Kwilt with no issue.
You can also easily use existing USB drives that have content already stored on them and connect them to Kwilt to make the content that was sleeping in drawers available and accessible again!