Environment & Energy

It isn't their job to determine which policies will be most effective.

In this case, the question was whether or not the executive branch had the power to do something without congressional authorization (or, better put, whether the existing congressional authorization covered what they wanted to regulate). For SCOTUS is was (while that determination was working it's way through the lower courts) whether one side or the other was likely to win in the end and whether (while waiting) the side asking for the injunction would be irreparably harmed while waiting for the decision.

It was thus relevant whether some power company would spend large sums of money (that could not be undone) complying with the regulation, only to later find that it was not within the regulators' power in the first place.