The new tool cleverly renders pages as a crawler would see it via a number of screenshots as well as providing High, Medium and Low warnings depending on the severity of blocked content.
This update is aimed at improving accessible content for crawlers and so is very poignant from an SEO perspective. The emphasis Google is placing on these blocked resources is a clear indication that this content is a ranking consideration (and if not now, it soon will be). This is confirmed by John Mueller, who made the announcement, who stated that blocking/unblocking resources ““sometimes plays a big role in how Google’s able to render & index a page for search”.
So there you have it!