I'd say it could. It gives one more inlet for hazardous files, though it is conceivable that anyone could just buy their own USB thumbdrive to try to subvert a system. But people could bring in stuff like small videos that couldn't fit on a floppy - either porn files or just funny little clips. Too many people don't have enough self-discipline to be able to only play certain files at the right times.
However, for bringing in files too big for floppies, or taking them home for work, USB thumbdrives could be an excellent solution. Fine balance between empowering employees, and risking misuse of the new power...