Read the person you are replying to. It doesn't matter if it is useless in real world. What matters is if it beats the tests created by govt bureaucrats.
>stop/start is estimated to boost fuel economy by 4 to 5 percent using the EPA test cycle
https://www.caranddriver.com/news/a19561461/automakers-incre...
It's not useless: a reduction in 4-5% of emissions in urban stop and go traffic would be huge for air quality and health. It likely won't do much if anything for total CO2 output but offloading the emissions to manufacturing of parts needed for extra maintenance (aka a far more efficient power plant in a less densely populated area) instead of driving can still be a net win.
Regardless, fuel efficiency standards have driven a significant amount of innovation even if this specific rule seems absurd from the outside.
During a normal 15 minute drive, the engine auto shutdown shaves maybe 20 seconds of runtime for me (smaller city without long lights) and it’s at the lowest engine consumption level (idle).
Given that an engine can idle for approx an hour on a gallon, I fail to see how an idle-off makes any meaningful difference for the average driver. It reeks of a marketing scam.