> So why not just do all the trading in the place where the authoritative copy is stored? That would certainly seem to be more efficient from the perspective o

> So why not just do all the trading in the place where the authoritative copy is stored? That would certainly seem to be more efficient from the perspective of minimizing the overall social cost. And what if trading on that exchange will stop for a couple of days for technical reasons? What kind of problems can that create to stock of large company, that can be traded only on that exchange? Or what, if the whole exchange will go out of business? Or decide to charge arbitrary large trading fees? Competition and diversity is generally a good thing. Tend to increase efficiency and minimize overall costs. That's valid for exchanges as well.