system
Given the following post, respond as if you're commenting on Reddit:
human
CMV: There is absolutely no reason to ever buy med grade gasoline.

Here is the deal.  If you car requires regular gasoline,  there is no advantage to buying anything better.  You car was engineered to run on regular and will gain no performance advantage from anything else.

If your car is engineered to run on premium gas, you will not only kill your performance by putting lesser grade gas in your car, you will run less efficiently negating the cost benefit of the cheaper gas.

I am not aware of any car sold that runs on mid grade.

I would love to know who has a good reason for the existence of  this useless product and who buys it and why.
gpt
The “octane” rating is also known as the “anti-knocking index” because it helps prevent knocking (if your engine knocks).

So let’s say you have an old car and the piston shafts are getting full of corrosion. Due to the presence of the corrosion, there is less space in your piston shafts. So when the pistons come down on the gasoline, the fuel is compressed too much too quickly and fires early. This leads to “knocking” sounds in the engine. Switching to a more compressible (higher “octane”) gas will help prevent the knocking.

Now, it may be that you find that mid grade works fine and so you save a little bit of money versus buying high grade.