Since GLI allows files to be launched in external applications, some of these apps may be editors as well. That means that imported files can be edited by users on the client side before building, while the remote GSDL server would be building the copy of the unedited files in its import folder.
In a more specific case, the replace_srcdoc_with_html.pl feature's whole point is to allow GLI users to import files, convert them to HTML, edit those HTML files and have then built with those edits intact. This works easily enough in the local GSDL case, as the files being edited and those being built are of the same import folder.
But when GSDL is remote, there's at present no way that the server end knows of edits made to documents using external applications launched from within GLI. Therefore, building still works with the unchanged server side copy of the import folder.