Trusted Constraints and NOT FOR REPLICATION
NOT FOR REPLICATION was indended for this scenario:


You have a Order table with a FK to Person table.
Order table is in publication no.1 and Person table is in publication no.2.
The Order pub and Person pub will happen at different times. Therefore if some new records were in the Order table were replicated down to the subscriber and the Person table was missing the person that new Order was for, you don't want the replication insert to fail at the subscriber. Instead, it can be trusted that the new Person record will come down at some point because the FK was used at the Publisher.
At the subscriber, if you insert an Order record, the FK will check that the Person record exists.


I would always stick with this policy and use NOT FOR REPLICATION only for that purpose of FK's relating to tables in different publications, and not for the purpose of query plan optimisation.