The benefit would come because we are currently using a great deal of natural gas to make power. This demand drives the price of natural gas upwards. The result is that petrochemical facilities that use gas a feedstock or need it for fuel must pay more and are less profitable. When the profit crunch is bad enough, the parent companies move the chemical plants to China, and Americans lose jobs.
I like clean air as much as anyone does, but if I have to choose between less than perfect air, loss of freedom to drive where and when I want, and loss of my job, I'll choose slightly more polluted air. For most of us, the difference between what is allowed now and what we'd see with slightly relaxed standards is a difference that we'd never notice. Those with breathing difficulties might have some problems, but even they will do better in an America that has good jobs as opposed to an America that doesn't have good jobs.
WFTR
Bill
We can use coal and have cleaner air. Really we have the capability to install "scrubbers" that clean the air better than what we breathe.