It's an engineering gain primarily derived from the gasoline component of fuel.
The accurate analysis of the situation is that no oxygenate is necessary in the vast majority of gasoline fueled vehicles on the road today, with properly refined gasoline.
Additionally, ethanol is grossly more expensive to produce than gasoline, and the subsidy revenue pursuit causes disasters such as the MTBE pollution scandal which purpose was to shift subsidy income from Archer Daniels Midland to more leftist politically connected chemical companies (many foreign) that manufactured MTBE from their waste products.
Gasoline oxygenate additives have NEVER been necessary for pollution reduction, and have always caused a net increase of pollution. It has always been about getting taxpayer funds (subsidies) to crony capitalist political donors, and never been about pollution.
And, too, there’s the niggling little detail that a “pollutant” is only a “pollutant” if it leaves behind the specific toxins you test for above permissible levels. So, if my chemical product leaves behind sulfates below permissible levels, and oxides of nitrogen below permissible levels, but also seven other toxins you don’t check for, then my chemical product is NOT a “pollutant” even though its probably more toxic, overall, that whatever “evil” chemical it replaced.
All that to say, the whole ethanol/MTBE charade involved WAY more than EVER met the public eye, and the refiners got rooked, big time. FedGov said, at the outset, they could use either ethanol or MTBE as an oxygenate, so they picked MTBE. Then, the same FedGov came back a few years later with the press saying “BAD refiners! You picked mean, nasty, inexpensive, vile MTBE when you could have picked beautiful, pristine, holy ethanol! BAD, EVIL refiners!”
There’s even more to it than that, but you get the gist.
Your government at work...