Google added an optimisation to Google Tag Manager (GTM) that lets containers send measurement data straight to supported Google destinations. Before, GTM loaded the Google tag (gtag.js) separately to do this, which added more JavaScript and could slow data down. Google says the change means faster pages, better data collection, settings managed in one container and easier troubleshooting. The catch: you have to optimise your existing container to use it, and it only works for supported Google destinations.
Every extra script on your store slows it down a little. One less one won't make headlines, but it's exactly the kind of small thing that adds up on a mobile product page.
The bigger win is cleaner tracking. When conversions go missing, the first hour usually goes on working out which tag fires where. Fewer layers means faster fixes, and a solid data layer is what every ad platform learns from.
This isn't automatic. Someone has to optimise the container, so it'll sit undone on most stores unless you ask for it.