The Expanded Row modal packs some powerful layout features, like multiple columns and full tables. But there just isn’t that much horizontal room, leaving those columns and tables feeling cramped. I’ve wished for those modals to have a true edge-to-edge fullscreen option (feature suggestion!).
I made a custom CSS hack to do it myself (shown here), but I think this would make a great true feature—perhaps in addition to the Content Alignment toggle in Page Options or something similar in the Edit Layout settings.