While I'm certainly no chemical engineeer, my understanding is that leaded fuel was designed as a lubricant for the valve seats in early days to prolong their service life. It was also determined to add noxious pollutants to the air, so it was banned in the 70's as a motor fuel for vehicles driven on the street. Race gas, and Av gas still have lead in their chemical composition for the same benefit, but are not outlawed due to a comparably limited usage vs the millions of cars on the streets. Using a leaded fuel in a car equipped w/ catalytic converters is a sure fire recipe for a clogged converter.
Av gas has detonation inhibitors that actually slow down the burn, and make it's usage in a race car/high compression engine less than favorable when compared to using the equivalent octane rated automotive gas (i.e. Sunoco 260).
Alcohol based fuels, (like the E85 I'm considering) burn even slower than AV gas, at at a much lower temp than gasoline. It also takes considerably more of it to do the same job.
Cars running E85 will get significantly poorer gas milage as a result. While fuel consumption is a definite con, the fact that it burns so cool makes the engine run significantly cooler, to the extreme that race cars powered solely on methyl-alcohol do not even need a radiator. The other, obvious pro is the potential 100+ octane rating. It's a very clean burning fuel as well, so the typical carbon, and crud that are by products of gasoline, is non-existent when using E85
Back on the con side, it's corrosive, and your equipment has to pump more of it. There is a very high percentage of moisture in E85, and that moisture typically ends up fouling the engine oil much more quickly than a gas fueled engine. That makes the stuff not compatible w/ every filter/pump/regulator/lines currently in use on a gas powered vehicle. That makes for a little homework to determine what has to be changed/upgraded when considering it as a fuel.
Now, I don't know how I did on my armchair chemistry lesson, but that is how I've always seen it.