What was the positive in putting lead in gasoline?

Improved gas mileage and performance because Lead stopped “knock” in gas engines.

It allowed for higher compression engines which gave higher performance.
“Lead,” or more precisely, “tetramethyllead n (1964) : a volatile poisonous liquid… used esp. formerly as an antiknock agent” -from Merriam-Webster’s Collegiate Dictionary, 11th ed.
In todays engines, other chemical compounds are used to increase octane and eliminate “knock” or preignition.

I’ve got 2 quarts of lead gas additive in my garage. I use to use in with my old 55 Chevy when they first stopped putting in gas.

In the early 20th century, automotive manufacturers were searching for a chemical that would reduce engine knock. In 1921, automotive engineers working for General Motors discovered that tetraethyl lead (better known as lead) provided octane to gasoline, preventing engine knock.

In short, it allows for better performance.

Lead increased octane and protected/lubricated the valves but was toxic and damaged catalytic converters.

I worked in the automotive industry when this transition was taking place and we made an interesting discovery.
If you mixed leaded gas, Octane rating 88, with unleaded gas, Octane rating 87, the mixture’s Octane rating was in the 91–93 range. The curve of Octane rating vs percent TEL, tetraethylead was not a straight line. It looked more like the y= sqrt(x) function.
It was a neat trick when we played with spark advance timing.

See this very interesting story: https://www.mentalfloss.com/article/94569/clair-patterson-scientist-who-determined-age-earth-and-then-saved-it

Wow bob.

@bob_ Thanks! That was a great read. I started in the automotive industry in 1974 and was brought in to work on and invent new pollution controls. Since we used catalytic converters lead was forbidden to be anywhere near our work. Good thing!

@bob_ : great article! Similar arguments are being used for Climate Change.

In addition to what @LuckyGuy said, lead did damage catalytic converters but catalytic converters weren’t put into cars until 1973, the first year they put out cars that burned only unleaded gas. Also that year, they made unleaded gasoline nozzles of a smaller size than leaded gas nozzles, and put restrictors into the gas tank filler pipes (just below the gas cap) so that only unleaded gas could be put into cars that had to have only unleaded gas.