The directory /var/spool/uucppublic is the one place in every system to which UUCP by default is able to copy files. Every user has permission to change to /var/spool/uucppublic and read and write files in the directory. However, the directory's sticky bit is set, so the directory's mode is 01777. As a result, users cannot remove files that have been copied to it and that belong to uucp. Only you, as UUCP administrator logged in as root or uucp, can remove files from this directory. To prevent the uncontrolled accumulation of files in this directory, you should ensure that you remove files from it periodically.
If this maintenance is inconvenient for users, encourage them to use uuto and uupick rather than removing the sticky bit, which is set for security reasons. See the uuto(1C) man page for instructions for using uuto and uupick. You can also restrict the mode of the directory to only one group of people. If you do not want to risk someone filling your disk, you can even deny UUCP access to it.