I am rolling out Chrome in an enterprise environment with 5000 Windows clients. In Chrome 66 it seems to be the case that the default settings for site isolation chrome://flags/#site-isolation-trial-opt-out means that we are opted in to a field trial? Does that mean it will essentially be a case of random chance whether or not a particular client is using site isolation at a particular time? Apparently Google have fixed the issues with printing iframes since the beta (although I haven' tested it). So my only concern would be RAM usage, as many have only 4 GB of RAM.