Consolidating Multiple Sets of Books

Hello,

We currently have several setsof books each attached to its own operating unit.  We would like to consolidate however, we woul like to understand the advantanges and pitfalls of doing this.  We are currently on release 12.  I understand that we could use ledger sets however,  I would still like to understand what the consolidation process effort would take.  I would like to clearly understand the steps in consolidating a set of books.  Do you create a new one and then consolidate all of the others with that one?  How do you consolidate all of the historical data? 

Any information you can provide would be greatly appreciated.