Rudder

Use case:
content of a file enforced - default for all groups:
toto
tata
${generic_variable_definition.GROUP1_ONLY}
${generic_variable_definition.GROUP2_ONLY}
${generic_variable_definition.GROUP3_ONLY}

Default Generic CFEngine variable definition contains:
GROUP1_ONLY=""
GROUP2_ONLY=""
GROUP3_ONLY=""

group1 Generic CFEngine variable definition contains:
GROUP1_ONLY="tutu"

group2 Generic CFEngine variable definition contains:
GROUP2_ONLY="tztz"

and so on...

This gives a better flexibility in the rules applied to group. If you have a group that contains all your nodes on which you apply the default variables definition, you can just apply per group variables definition with lower priority while still using only one "content file enforcement".