To get the full benefit of it make sure you fill your tank up with gas then put the alcohol in. It will wake your car up if there is alot of water in your fuel.It will take all te water out of your fuel .I do it every fill up big seat of the pants difference.Just my opinion.
Most blends of "Heat" (winter fuel de-icer) are made out of Isopropyl, I believe. You do not get the same effect as injecting it, if that is your intent.
Its not good to use it as octane booster. Xylene or race gas would work much better. That much alcohol will kill your pump/injectors/any rubber it finds
We used to do that back in the 70's if you suspected having water in the gas tank. It basically "dries" up the water. Kinda like if you drink too much booze, it "dries" up your brain.