News Courtesy of Yoast.com:
Why is readability important for SEO?
It is unclear whether readability is a specific ranking factor. Therefore, we don’t know if Google uses tools like the Flesch score (or a variation of it) as a ranking factor in its algorithm. However, we do know that, from a holistic SEO perspective, readability is very important.
If your text is very complicated, the text will be too hard to read for your audience. This might scare them off and make them search elsewhere for information. In other words, impenetrable text can result in a high bounce rate, leading to lower rankings in the long run. So, you should make sure your articles are well written and not too difficult to read.
Ryan’s Take 
I’ve discussed on several occasions how I believe readability is just as important as SEO. Since search engines are becoming more human-like, there’s been an emphasis on creating quality content over the last several years. Keyword stuffing and article-spinning are relics of the past. Even though that may have worked a decade ago, today it just looks very unprofessional.
If you want to have success in building your business or brand, you have to provide useful and unique content. That’s not easy if you’re in a crowded industry. There are thousands of websites of businesses that offer services like legal, plumbing, accounting, etc. Unfortunately, with such high competition, most of the pages for those businesses will be buried in the search results. In order to separate your business from the rest, a lot more information is required than just what services are offered.
For instance, some of the top electrical companies in the search results go into detail about explaining different types of wiring. They may also provide “How-to” articles for easy things like replacing an outlet cover. Content like this is great for checking off the useful and unique box I mentioned earlier. However, if it is written in long-winded sentences with technical jargon, it may as well not even exist at all.
It’s for this reason why I value the readability analysis so much in Yoast SEO. It basically forces you to keep sentences short and to use common words over technical terms when possible. Then, of course, there is the passive voice. This is perhaps the most difficult readability test that I have trouble with. In effect, it advises you to speak in a more authoritative tone.
I’d suggest that you write your content first and then go back and make adjustments rather than try to do so on the fly. It might be an inconvenience but if it keeps your audience engaged, it’s well worth the time.
