My system is set up so that my drive folder is on a separate partition. I have a clone copy of my main system partition so that if the system crashes I can restore it, or so that I can copy my system partition on a new computer. I did the latter - on an formatted laptop with two empty partitions, I restored my system partition, which includes the insync installation and config files. I expected that insync will automatically download all of my files to the new computer, as would have happened with a clean installation. Instead, it deleted all of the files on the server of my google drive! Thankfully, I managed to restore them on the server side, but this can potentially cause data loss and huge problems.
EDIT: I tested it, and the same happens on a clean installation if I first copy my old home folder to the new computer. I guess that insync config file assumes that the files should be already on the hard drive, and since they are not, it thinks they have been deleted and it deletes them from the server as well.