But energy consumption could be different for this hypothetical 0.5 and 0.9.

Energy consumption wasn't really a concern when the idiom developed. I don't think people really cared about the energy consumption of instructions until well into the x86-64 era.

	▲	allenrb 5 hours ago \| parent [-]
		Not sure why this is being downvoted, but it’s absolutely correct. For most of the history of computing, people were happy that it worked at all. Being concerned about energy efficiency is a recent byproduct of mobile devices and, even more recently, giant amounts of compute adding up to gigawatts.