Hi Sathish,
We chose this model as we needed our Legal Entity in the Entity Dimension for Intercompany Eliminations, but we manage the business primarily by Location and Department, which is our U2 and U3 respectively.
Our route to getting where we are today was not straight forward. We went live last year with a very simple model, with almost no security by U2 and U3. However, management once using the system and to provide more self service to data, which includes employee comp, decided we needed more granular restrictions. This lead us to our current model over the last year.
We do little workflow security since most data is loaded by automated processes, or entered via forms.
For maintaining our growing 4.5k user base, our IT group used an API to auto create each night users meeting certain criteria and auto assign them to a specific group. Do not know specifics how they accomplished this. This has been a game changer from something that was going to be manually maintained.
Hope this helps!
Agree security has been a challenge for us too, especially with how granular we have gotten, which requires new groups and slices rather frequently with our growing business.
Does Flex have two environments? Have found that to be critical for developing a model like we have.