Dean A watchdog is a special timer that runs independent of the OS or a process to ensure that it doesn't hang or take to long to complete. If the watchdog runs out of time, it is typically supposed to prompt the OS to kill the running program or at least prod it to finish up.
Setting those values to 0 tells systemd not to use the watchdog timer and allows the system to take as long as it wants to finish up, though that may also require a manual reboot or shutdown to recover. So no, despite @just meaning well, generally this wouldn't be the solution to a hung system since that is exactly what a watchdog is supposed to prevent.
My best guess is that some systems (like @Brucehankins') have a faulty interface to the watchdog timer through the BIOS/UEFI firmware or kernel drivers. In which case, what is actually happening is that the system hangs while trying to set the watchdog timer. Configuring a timeout of 0 tells systemd to not bother with the watchdog at all, avoiding the hang, and finishing the shutdown as expected.