By default, Squid will send any non-hierarchical requests
(not cacheable request type) direct to origin servers.
When this is set to "off", Squid will prefer to send these
requests to parents.
Note that in most configurations, by turning this off you will only
add latency to these request without any improvement in global hit
ratio.
This option only sets a preference. If the parent is unavailable a
direct connection to the origin server may still be attempted. To
completely prevent direct connections use never_direct.