I trade on only 1 exchanges. Other exchanges i use as a comparison only. Due to the length of confirmation process makes it difficult to move balance from one exchanges to another exchanges.
It doesn't really take that long and you can have a portion of your wealth on different exchanges. The most typical example and reason for this is if you want to invest in a coin that isn't on your primary exchange. That's why I use bitfinex, poloniex, bittrex, kraken and liqui all at the same time.