Precedence can be tricky in certain scenarios. Imagine you want to make FIM master for a given attribute, but you need an initial flow from another data source. A good example is the LDAP distinguished name. If you have a rule that builds the DN automatically based on a base DN and one or more attribute values, the object is provisioned with the correct DN on export. But when you want to visualize this DN in the FIM portal, you need to be able to flow it back. If FIM is master over the distinguished name attribute, this flow will be skipped "Not precedent".
So you have to consider the option of using equal precedence, since manual precedence is not possible in combination with the FIM MA. But equal precedence is dependent on the synchronization cycle order: "the last one to write the attribute wins". Therefore it is not an option if FIM needs to be the absolute master of the DN attribute and you want to make sure that it always has the value you expect it to have.