I just wanted to share my thoughts:
Account Segments are simply real. You are going to have separate accounts for specific entity and that means you must be setting these accounts up on several other places in GP other than only Posting Accounts setup. For instance, if you are going to have accounts for each employees of your organization and you track expenses on them, then you got to have each account setup against each employee explicitly and setup GP such that it takes accounts from employee directly instead of Posting Accounts.
Analytical Accounting is purely logical. You don’t really have separate account for each entity that you wish to. Setting up AA dimensions and codes are one time.
Actual complexity lies in assigning AA codes on a particular transaction. Worst case, if you have an apportionment across different AA codes, you have manually apportion it in Analytical Accounting Transaction Entry form. Data Entry is very complex at times with AA. Without proper AA setup, your data will logically scattered and any analysis on this data would be a menace for you to understand.
You can minimize the data entry time by using Analytical Accounting ALIAS, but that again depends on case to case basis. You cannot always depend on AA ALIAS for all kinds of transactions.
Simply speaking, AA considerably reduces your COA but let you toil at times entering apportionment within a transaction. You gain on one side, you have to experience some pain on the other side.