By default, accessing the search interface requires specifying a profile
via the pr query variable. Methods of choosing which profile to search if
no profile is specied can be selected here. The Default Profile setting is
used if none match. Currently the only option is Hostname which allows the
selection of profile name based on the hostname used to access the search. If you
are providing search for multiple departments or other groups, and give each a unique
CNAME alias to the server then you can create profiles based on those aliases.
See Using Default Profile Sources Hostname 4.15 for more details.