Also, lets assume that you trade for example a future that is open during most time frames.
During say market hours, the bid / ask can be 1 tick apart, but during after hours the bid / ask can be 3 or greater ticks apart.
This means you are paying $ 30 cost to trade after hours. Even worse, let's say you get stopped out on your trade. During normal hours your stop should function correctly getting you out with no slippage to at most 1 tick of slippage, but you could get stopped out due to low volume after hours with an extra 4 ticks of slippage on top of the bad bid / ask spread.