30 July 2016
All Member is a very handy member to use in some MDX calculations. There is a need to remember, when you drop any measure and no other dimension members, it doesn't mean that they aren't in use. Every cell (tuple) has a coordinate. If you don't select any member from the hierarchy it doesn't mean that your current coordinate is unknown, it is .DefaultMember, most likely it's .All member (you can change default member in the Attribute properties).
27 July 2016
I expect this post will be updated over time. Here I want to describe my test DB to handle business cases.