This seems like a sort of complex trade-off (taking your word for it that they do run more efficiently when run continuously). We’d still probably prefer to run them on renewable energy and defer them when running on non-renewables, because the inefficiently consuming a plentiful resource that is not very damaging to produce, is better than efficiently consuming one that is destructive to produce.

But if we have multiple tasks with multiple levels of defer-ability (either due to efficiency benefits or due to people just wanting to run their dishwashers at a time convenient to them), it could be more complicated. But working out trade offs like this is what the market is for, right?