Short notes after ZBXNEXT-4019 implementation: frontend user is still able to set own refresh intervals in the small drop-down list.
Problem: if the user is allowed to modify the dashboard and he sees the new settings in widget configuration, it's not very clear why changing the refresh in widget settings does not change the actual refresh in the list.

What I'd suggest, is to extend user's drop-down list by a selectable line like "Parent's (NN seconds)" or "Inherited (NN seconds)".
When user selects it, related "web.dashbrd.widget.rf_rate" record should be deleted from "profiles" table.

Then it will be more user friendly and much more clear.