Generally the lower margins for bonafide spreads reflect lower volatility. In general, its all the same in the end. If you trade volatile spreads, there is more potential for big gains, and large losses, thus the margins are basically similar to two outright positions. If you trade less volatile or exchange recognized bonafide spreads, you need less margin. Generally here the reward is lower and so is the risk.
Unless, of course, you are really good. Then your experience tends to bend the above generalizations.
Unless, of course, you are really good. Then your experience tends to bend the above generalizations.