CUBEMEMBER not returns #N/A for something that doesn't exists in the model

I notice that if I change & to ALL it works, but I didn't understand the logic

=CUBEMEMBER("EDPModel"; "[FCT_FIN_CONSOLIDATED].[NM_REPORTED_RECURRENT].[ALL].[Personnel Costs Adjustments]")

I would like to understand cause I need to justify this change that my customer must to do.

Anyone?