I guess there will be no special cases are needed for the reason of margin trading for whether to keep your coins within exchange overnight or not. You may simply go for your usual practice of what you do with your capital. I do trade only with few major exchanges like bittrex and binance, still I do not prefer keeping my funds there hence I do withdraw time to time and will go for re-depositing whenever needed. At the same time, right now I am having more than one bitcoin in bittrex. I have bought TRX for airdrop and until last night I did not receive my share of airdrop and hence still holding there.

If you are an active trader and you are trading with highly reputed and old exchange then you may not go for daily moving out your funds. I am not active trader hence I do not keep funds within exchanges for longer time.