System users are those used to run services such as DNS, mail, web servers, and so
forth. The reason for this is security; if all services ran as the superuser, they could
act without restriction.
Examples of system users are daemon, operator, bind (for the Domain Name
Service), and news. Often sysadmins create httpd to run web servers they install.
nobody is the generic unprivileged system user. However, it
is important to keep in mind that the more services that use nobody, the more files and processes that user will become
associated with, and hence the more privileged that user becomes.