LE in r12 and 11I.

 In r12, when you define a ledger or accounting setup, the legal entity is not mandatory or it is optional and can be defined later. And the system says that if you are not doing the intercompany accounting, then it is not required at that point of time. 

However when we define an OU in r12, and when we enter the operating unit information, then legal entity is mandatory, along with the Ledger.

so that means legal entity is required to associate an OU to a Ledger. my understanding is the legal entity link is broken in r12 between OU and Ledger.