The file contains AppleTalk protocol updates. AppleTalk is found in ROM,
but when an update is made to AppleTalk, these changes get put in a system
file. This could happen if you're doing a number of system-related
installations: 3Com, EtherTalk, System, etc.
The 3Com INIT is, unfortunately, not "smart" enough to say "I'm not on,
EtherNet, so don't load yet." If you forget to disable the 3Com INIT and
you boot with LocalTalk selected, you will get a bomb and have to boot from
another disk to start up.