It's worth doing when the -true cost of resources- is represented in their price.

If it's not, then more of the thing ends up being done than is socially optimal.

E.g. artificially cheap agricultural water -> lots of water-heavy crops being produced like alfalfa and exported for less than the cost of the water.

I think we might disagree about the degree to this is true, but I think most of us can agree that the true cost of energy is not completely included in its price.