The backstory here is that huge amounts of Chinese money flows out of the country without the consent of the government. Apparently, around $816 billion was expropriated from the land, both by private citizens and officials with their hand in the till. It's believed that Macau is an easy escape route for the cash, since folks can pull out cash, ostensibly to gamble, place a couple of trivial bets and then send off the rest.
It's a move that shows the very different expectations of privacy and liberty in different countries, imagine the reaction if the US attempted to do the same. Although if China can demonstrate to the world that its system stops money laundering and protects banks against fraud, there's no telling who may like the idea. Not to mention that since US law enforcement agencies already have a facial recognition database, perhaps it's already going on.