Google’s John Mueller said in a Google Webmaster Help thread that it makes most sense to keep the default setting found within your content management system for your robots.txt access control.

This answer comes in response to someone asking if they should block or allow access to the admin portion of their WordPress site.

John said, that generally, you want to keep the default setting. This is now espesially true for WordPress sites, they are pretty search engine friendly out of the box.

John wrote:

So use Search Console and if you see issues, then tweak it but otherwise, keep it how it is.

Forum discussion at Google Webmaster Help.