This feature is to forge recording according an ACL, sur you can forge it globally using the computers section but in some cases, you need to forge a record according sources IP addresses.
If you did not want to create an ACL object for destination domain and record, use it directly in the rule
Here an example :
If source is 192.168.0.0/24 and query is *.google.com, then the dns reply should reply to 172.0.0.1
Note: with service pack 679, you can use the “dst” object to specify multiple IP addresses.