My engine is designed for it. Being a TEOTWAWKI prep type guy the main advantage of it is if I had 150 gallons of gasoline post SHTF I could make or barter for 850 gallons of ethanol and have 1000 gallons of motive fuel.
Other than that it’s almost never economically feasible to use it because it knocks off about 15-20% of the mileage (less energy per unit of mass), and add to that the fact that the state bought a bunch of E85 vehicles and most places around here (bay area) charged $4-$5/gallon for it because they knew the state vehicles were a sure purchaser at gross overpricing.
This H&N market near one of my jobs is selling it for $1.99 though, and that is $1.25 below the cheapest gas around which is all 10-15% ethanol anyway.
There’s a station out near my Nevada land that sells pure gas and it’s usually 50-60 cents cheaper than California gas in general. I always get 40-60 gallons of that out there plus fill the truck. Whatever I don’t use in coleman lamps, old engines (hobby) and work genny I rotate through the truck on the next trip out.
I should get a carb jetted for E85 to put on a generator, or find an old Witte, IH, etc... that will run on heavier fuel and rig it to a generator. The only downside to them is they generally weigh about 200 pounds per horsepower LOL.
Years ago I did some experimentation and used 10 oz.of lacquer thinner per 10 gallons of 87 octane and my van ran like it was brand new! It had more pep, got batter mileage, ran so much smooter etc. it was truly amazing.
Don't know why I ever stopped.