Kind of. It's like hibernation but they dont normally hibernate. So long term, its not good as it lowers their immune system but short term, it doesnt hurt assuming you dont have a cold AND wet cage. That can trigger a RI just like hot AND dry can too.
As far as energy efficiency, i dont think they can be more efficient than they already are. My snakes tend to not do much unless they smell dinner or have taken a poop or piss and are trying to get away from it lol.