Re: Subaccounts over having accounts on different exchanges
Other than that I don't see any point in subs. I also don't see the point in many exchanges. Open a few for sure to see, choose one you like, done. Unless you treat trading like casinos and are using all of them to do promos and bonus etc. 
Some people prefer more exchanges because they do not want to have their trading coins only on one exchange, they prefer to distribute the coin on more exchanges. This is because they think an exchange can be hacked and they do not want more of their coins to be affected.Some people use more exchanges to know which one is perfect for them. The exchanges are different in one way or the other.