Assume you downloaded X-Plane 11 for Linux (which is a few GB). Now you want to try it on Windows. Obviously you don't want to download 99% of the same files again. So you copy the Linux directory to Windows and run the installer. (that you downloaded)...
Unfortunately the Installer just wants to download another copy, refusing to accept the existing copy as update target.
The advanced user hacks some text file to make the installer know about this X-Plane directory, and then the installer is actually updating the Linux version to Windows, saving at least one hour of downloading.
I wonder: Can't the installer be extended to locate (register) an X-Plane installation? That wouldn't do much more than adding a line to the forementioned text file.
Also can't the installer have an option to download files for a platform different as the current one (assume you want to download versions for Linux and Windows in one directory)?