I guess the word here is significant. It certainly was used where it made sense. In the CAD group, we had simulations that might run for a few days. We used to call the mailer every so often to send status and sometimes do something like a checkpoint. It lead to Sam writing syslogd, particularly after Joy created UNIX domain sockets. But I can say we used it a number of places in systems oriented or long running code before syslogd as a scheme to log errors, deal with stuff.