https://almanac.httparchive.org/en/2022/css is an example page that loads a LOT of embedded Google Sheets charts in iframes with loading=lazy so that, browsers that support this, will only load the content needed near the viewport.
On Chrome this loads 1.7 MB of resources for the above the fold content (6.3 MB uncompressed). As you scroll down it loads more as needed. This is similar in Safari Technology Preview.
On Firefox this loads 32.06 MB of resources for the above the fold content (110.82 MB uncompressed) as it loads the whole thing (though this is with the default Disable Cache option ticked, it's a lot less than that with that unticked as there's a lot of duplication in these as a lot of the same JS is reused in each graph).
As well as downloading all that extra stuff, the browser has to process it, which could cause other performance issues.
I also got a complaint about this from a Firefox user: https://github.com/HTTPArchive/almanac.httparchive.org/issues/1822