It's a great plugin but if you have a lengthy keyword specially above 3/4 words, then you should not keep the density above 1%. For instance, if your word is "how to make money online". It constitutes of 5 words. In a 1000 word article, if you repeat it 10 times to come on par with minimum 1% density, Google would deem it as OVER OPTIMIZATION. IMO the actual density would be 50/1000 words, 5% which is way too much high.
You would be hit with a penalty and your page won't rank. Its one of the reason, sites like howtogetridofstuff.com have suffered in the recent past. All the EMDs also suffered because their content was over optimized. Besides, Google now wants to see diversified keywords. I would strongly suggest you to use variants of keywords.