PRE_REMOVE is used to prepare a spell for removal. This is only necessary in a few special cases.
An example from the "shadow" spell:
# Restore /etc/passwd when dispelling shadow ${INSTALL_ROOT}/usr/sbin/pwunconv && ${INSTALL_ROOT}/usr/sbin/grpunconv
(done in PRE_REMOVE because those commands are installed by "shadow", thus aren't available after the dispel)