Hey Stephane @ultramarineblue, hey all,
I agree with @Matticustard and @Ruairisdad. When you use a remote computer to run the Onefinity User Interface in the web browser of your choice, and you want to upload a file to the Onefinity Controller by clicking on the upload button, you get a window with the filesystem of your remote computer. You are free to store your g-code files where you want there, including using subdirectories.
So there is no need to use a USB drive to bring your g-code files to the controller 
, for this you have the Ethernet cable or the WiFi to connect a remote computer.
I would delete the g-code files on the Onefinity controller regularly (except those that serve as often-needed macros, as macros are not yet implemented1 (rsp. not yet backported from buildbotics)) and upload the g-code file that you need to be milled at the occasion.
The second advantage on using a remote web browser is as remote computers usually have a more capable graphics card with 3D-accelerated drivers installed, the built-in 3D toolpath simulation is shown, which is a very nice feature of the Onefinity/Buildbotics Controllers (note: the author of the buildbotics.com cnc system is also the author of camotics.org toolpath simulation software).
