Mainly in the carburetor days, but still around with fuel injection, sometimes people will put dry gas in the tank, about 12 oz of it, which is basically alcohol, which allowed any water that may freeze in cold temps to ‘dissolve’ into the gas and be eventually brought through the engine and out the exhaust. At least that’s how I think it worked.
With gas-ethanol blends, which is already alcohol in the gas, is dry-gas needed anymore?
When the ethanol sits, it is a BIGGER problem. I know, because my boat requires an additive whenever the ethanol sits in it. The composition (due to lack of additives now) has changed over the years, and ethanol will get water in it, and you need to be aware of it. Non-issue if the tank is emptied regularly (via use, etc)
No, absolutely not. The dry gas is for all practical purposes ethanol, and you can actually cause some damage by adding it to fuel that already contains ethanol, since it will raise the total ethanol concentration.
As Philster says there are similar problems with ethanol fuels, and in something like a boat or an older car that’s sitting for a long time and doesn’t have a well-sealed gas tank, you might want to add a fuel stabilizer, but not an alcohol-based one like dry gas.