Many SEOs care still extensively around the keyword density, the more the better. Previously this was quite a positive measure to tease out even more from the targeted keywords, today, this type of optimization, however, quickly go back off.
The keyword density does not specify the distance between the keywords on a Web page where they occur, and which followed the main theme. The KD(keyword density) has therefore not directly do anything with the quality of the content and relevance.
More than 50% of all searches are unique and are based heavily on the cherished long tail keywords. Often, visitors can reach you never expected, and often are exactly those surfers, the most valuable of all. Now if one focused around the SEO keyword density, takes care can lead to the elimination of the long tail chains. The description of the actual subject is suffering from the focus of the targeted keywords that are often whole sections removed so that the text is as relevant as possible.
Natural texts, however open the door to the unexpected long tail traffic and the search engines before they come above all, less suspicious. In the optimization towards the KD(keyword density) to quickly hoist one or other red flag at the crawlers at the end and scored significantly less traffic than with authentic texts. Stay natural!