What do airlines pay for FF miles?
 

When I buy/fly a Oneworld airline and post the miles to a different airline, is that good or bad for the selling airline? For example I fly BA and post the miles to QF, is this profitable for BA or QF (or both, thanks to the tax codes in their various countries)? Some airlines seem to actively encourage posting miles to another plan (e.g. CX suggests using AAdvantage for North American members). Are they being nice to AA, or do they make more money letting AA run the plan (and book the future liability for the FF miles)? I wonder whether there is significant cross-posting activity (I suspect it is very small, less than 1%) and whether the transactions are a wash at the end of the month.