Why does exchanges get quote updates from another exchange when the stock isnt listed on both?

This question might be pretty obvious, and I looking forward to the explanation.

The HFT's got an edge, because their processing power and speed is superior the exchanges.

But the thing i dont get is, why does fx. NYSE have to update NASDAQ with quote updates in the first place? Many stocks isnt cross listed, so whats the point?

I get that its important to deliver the NBBO, but if the stock isnt listed on a specific exchange, then whats the point sending quote information to it.

Submitted August 17, 2015 at 06:53AM by -Matis- http://ift.tt/1DZNJTc