The advantages of having more exchanges is that it will produce a competition among all exchanges to prove who is the best and the more competition will occur the greater service they'll provide and that would be a some sort of good news for us customer. However, this will be a nightmare for newbies because it can cause confusion since they had no idea that much with regards to qualifications of being a good exchanges.
In addition it is a sign of a growing market as these exchanges would not start their business if they are not seeing a potential to be profitable in the market. Though there are already good and more liquid exchanges in the market, there are still people who are using small exchanges as not all the coins and tokens are listed in big exchanges, there are small projects that can only afford to get listed in smaller exchanges so there's an equal opportunity for every exchange to gain clients.