Structure of SAP for BPC Cost Center Planning

Everything in SAP can be determined.  Final design can vary significantly.   One of my favorite questions to ask a would be consulting in FI CO is

"I have company code A and company code B.  I have cost center 1 and cost center 2 both associated with company code A.  In general ledger document entry for company code B can I enter cost center 1 or 2 and post the document within the standard capability of SAP?"

Let the fun begin when people try to answer this.   I know FI CO consultants that have been so called SMEs for years that do not know the right answer to this question.  They grew up technically and not from a business perspective.

How do you learn FI CO in SAP really?  How do you understand the structure of Cost Center Planning from an SAP ECC perspective so that you can create the correct design in BPC?