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.
I guess it's a good thing to have btc balances on several exchanges and trade with it on those platforms though transferring balances from one exchange to another would be quite challenging. There are exchanges that take a long time and the fees are more expensive right now compared to last year. I trade in yobit, polo and sometimes in bittrex but i don't transfer balances anymore. They stay where they are and i just trade in their respective platforms.