About automatic page layout algorithm, can we trust the "fetch as Googlebot" from the GSC ? I mean, it shows how Googlebot saw the page, for mobile/desktop . Can we be sure that this is what is used for a page layout analysis ? My worry is that some CSS3 / HTML 5 elements, if badly interpreted (old parser) can render the page layout wrongly.
What are the downsides of doing so? Less potential impressions?
Presumably, yes. Also, while the speed stats might look better, perceptually the site might appear to load slower because the ads fill up the page later than they might otherwise, so I'm not sure that's always a good idea.