[Jach]

GTM is just another JS CDN, like unpkg and jsDelivr and others I forget. What amuses me is sometimes a site will use all three. Often, none are necessary for the core site to work; having had to help add support for GTM once to a site builder product, I think the target demographic is PMs who want to add random marketing/ad/analytics/audience-segmented scripts to a site.

Very rarely it'll happen that I'll care enough to go through the list of possible domains to temporarily whitelist before finally giving GTM a shot, then immediately remove the whitelist. Usually I don't get that far, especially because if it hasn't worked by then, enabling GTM doesn't tend to work either, it's just a bad site that isn't actually providing what it claimed to provide. NoScript has never disincentivized me from visiting a new site, but it has made me give up on some or look for alternatives. My daily experience is pretty minimally impacted by it. (Still, I don't usually bother installing it on work machines or my travel laptop (which is remoting to my home PC most of the time anyway), and sometimes I'll just load the page up in a chromium tab (incognito or not) rather than play the game of five refreshes from whitelisting JS.)

The performance impact is quite minimal I think, especially if you compare the difference between Firefox with NoScript and Chromium without, the latter is just faster because it's not Firefox. The oldest machines I still use sometimes are from 2009 (with an i7 920, pretty good for the time) which as my old daily-driver I used NoScript, and 2017 (my travel laptop with an i7 7820HQ) where I don't bother. Neither is all that slower for web stuff than my current daily driver with a Ryzen 9 5900X. The web is just slow even with newer hardware. (In contrast to others here though, I immediately notice the difference of better hardware with local applications, especially content authoring ones like gimp or krita.)