Operating Concern are created in a CO Code and are used to 
do analysis on PCA (Profit Center Acctg) / CO-PA. OP 
Concern used for performing these tasks which are time / 
project based / event based (like Advtg Mktg Exp, Training 
Exp. Etc.)for the analysis of parameters, like measuring 
internal profit of a SBU, Sales data analysis (COPA).They 
can even be used for Analysing balance sheet items 
(Stocks,Assets,cash etc.)

The controlling area is used for Internal Cost measurement. 

The Contolling activities (Like - Expenses, Cost objects, 
Internal Orders (Cost Elements), Production orders etc. 
need to be created and assigned in a Controlling Area for 
that co code.  Generally, You define One Controlling Area 
and Assign that to the Co Code. However, you may have more 
than One Controlling area, but Best practices suggests to 
keep one controlling area for ease of configuration. 

Please correct me if I am wrong.