The most important reason Google needs to have these resources available is so that websites can be more mobile-friendly. By unblocking JS and CSS, webmasters would actually be helping improve their mobile sites. Rendering these resources to Google also helps Google better identify websites that are using sketchy SEO tactics or highly visible ads and ensure that they are demoted or removed from the rankings.
This can seem a bit overwhelming at first, but there are few key factors you need to focus on when unblocking JS and CSS. Webmasters should note that their homepage is the most important page regarding these resources and it should be your first priority to allow JS and CSS on this webpage. It is also crucial for webmasters to make sure that all resources are unblocked on both the desktop version and mobile version of their website.
However, if you area blocking entire directories then you would need to use something like this instead: