(I am working with an updated version of concrete5 5.6.1.2 to concrete5 5.6.3.3 ... in the 5.7 version I do not believe this is an issue)

The problem:
In the robots.txt, the themes map was disallowed to be indexed in the 5.6.1.2 . (in the 5.6.3.3 this is allowed)

Question:
Is there a reason to disallow the indexing of the themes map in the old version?
Are there any downsides to allowing the themes directory to be indexed by commenting out the disallow in the robot.txt?

Background story:
Now google will rank the mobile friendly websites better than the non-mobile-friendly websites.... you can test your website at :https://www.google.com/webmasters/tools/mobile-friendly/...

My websites are created using bootstrap 2 so I though it would not be a problem..
However, because the bootstrap.css and bootstrap.js resides in the themes map (which is not allowed to be indexed), google says my website is not mobile friendly (in the test). When I comment out the "Disallow: /themes" in the robot.txt then the test-tools says my website is mobile friendly.

So my question: Are there any downsides to allowing the themes directory to be indexed by commenting out the disallow in the robot.txt?