Pingjincang, the futures contract bought today, is sold today.
These two points are reflected in your trading system. First of all, their risks are different. If the futures are overnight, the risk is likely to increase. One more thing, their handling fees are sometimes different. For stock index futures, the handling fee is only 0.23/10000 when closing positions every other day, and it is as high as 4.6/10000 when closing positions.