The ONLY reason I check density is to give myself an indicator of my overall usage of my primary key phrase.
Often people are shocked to discover that they have not used their key PHRASE as a whole anywhere on their page. They have bits and pieces of it, but have neglected to use the full phrase together within their content. It is pretty tough to convince the search engines that your page is about the selected topic when you don't include it within the content. (Unless you have a TON of incoming links using that phrase.)
On the opposite end of the scale people OVERUSE their key phrase and it no longer comes across naturally. Taking a quick peek at your density will let you know this also.
The key is to find BALANCE in your content. It is not about density. It is about focusing your writing on a specific topic.
Just my
