There are a lot of self-declared "optimized" robots.txt files for WordPress around the web, but most of them don't allow full access to most Googlebots that scans our website for various reasons, such as: mobile browsers compatibility, PageSpeed insights, tag/structured data analysis, & more. Here's a list of all of them as of October 2016, including the most recent ones.
If you want to be sure that your robots.txt isn't blocking any of these, you can test your website URLs with the following tools:
- Mobile-Friendly Test: https://www.google.com/webmasters/tools/mobile-friendly/
- PageSpeed Insights: https://developers.google.com/speed/pagespeed/insights/
- Fetch as Google (requires a registered property in Google Search Console): https://support.google.com/webmasters/answer/6066468?hl=en
If you're unhappy with the results, I strongly suggest to adopt something similar to the following:
That's it for now: happy SEO!