I found a really interesting use-case for using the 'lookup multi value' switch in an augment transformation for the global firm I currently work in. For simplicity's sake, let's say company X has 4 external vendors in APAC - Singapore, Thailand, Philippines and Vietnam. Each of the 4 AE's should only see opportunities that they serve. The not so easy part is that the 4 are NOT the opportunity owners and are linked mainly to the oppty by region. Graphically it looks something like


Oppty   Region Oppty Owner
A           Vietnam       John
B           Philippines   Jill
C          Singapore    James
D          Vietnam        Henry


The 4 external vendors are
Kyle , Rob    Vietnam
Rudy           Philippines
Sam            Singapore


When Kyle logs into Salesforce, he should only see oppty A and D  /  Sam should only see oppty C.


q: How can this be implemented given that the only link between the 4 to any opptys is thru the Region field?
a: Create an excel sheet listing the 4 vendors and their regions, bring it into Einstein , load it as an edgemart node THEN
AUGMENT IT TO THE OPPTY OBJECT USING multi-value joined by?...... Region


Afterwards, you would end up with a table like this.
Oppty Region  Oppty Owner  Vendors
A      Vietnam     John           [Kyle, Rob]
B     Phil             Jill               [Rudy],  etc..


After you build this table, next and last step is to register the dataset and attach this as a security predicate (in pseudocode):
'Vendors' == "$User.name"