Note the following
If you have a master record Foo__c with a detail record FooChild__c and a RSF within Foo__c that, say, counts the number of FooChild__c (
- With a workflow on Foo__c defined to run every time Foo__c is created or edited where
FooChildCount__c > 0
- Will execute the workflow each time a FooChild__c is added as this causes the RSF field to be changed and hence the workflow will execute
The RSF need not be a Count operation; if it is a sum or avg/min/max and the rsf field changes because of a DML operation on FooChild that alters a value used in the RSF calc, the workflow on the parent Foo__c will fire provided its condition is met.
So, while workflows won't fire on recursive updates as per Triggers and Order of Execution, it is not clear from OP whether recursive updates are in fact the transaction in question.