When I have tried using cameyo on a virtual machine to make a portable copy I find on using the result that data is dropped into C:\Users\Username\AppData\Roaming\VOS.
Is this always the case? How can it be used to avoid this happening?
Yes, necessary files are extracted to the package's repository. The default location is %AppData%\VOS. If run from a flash drive, the files will be extracted to the USB SSD. With Package Editor, you can change the default location of where the files are extracted (Data storage under the General tab). By running the package with -Remove parameter, the repository will be deleted. Documentation here.