It may not make sense to choose your primary airline for this benefit.
This feature was added when American Express's contracts for access to CO and then AA lounges ended. The idea was that they would give us $200 toward the cost of an airline club membership, and they allowed it to also be used to reimburse nuisance fees for services (e.g. seat selection, checked bags) that used to be bundled into ticket prices, because most airlines don't operate clubs, not everyone uses them, etc.
I thought about changing m airline of choice as well for that very reason. My situation is very close to dkmatter. Based in Houston/plat with united/have the legacy united presidential card & sw companion pass. BUT, don't we also still have the extra points back with our airline of choice bonus to think about? I mostly fly United internationally and southwest domestically - that is the only part of changing my airline of choice that has me perplexed. So here I sit...still unsure how or what to do or when to do it!!