Keyword stuffing. Pick half a dozen key terms and litter them liberally around your website. What does this do for you? Mostly, it restricts the vocabulary of those who find your site.
Using high density keyword strategies and related strategies which optimize a website for just a few terms are kind of like assuming your audience has a 500 word vocabulary. Not really a wise assumption, given that the average native English speaker suppsedly uses between 1200 and 2000 words in everyday speech — and that this number is estimated to be 10 percent of their known vocabulary.
These statistics on vocabulary are an interesting question of their own, as an aside. It’s well worthwhile to question the veracity of that statistic. I suggest reading How many words? by Michael Quinion to get a sense for the true complexity of the question.
Regardless, by focusing your research on a narrower body of keywords all you’re doing is restricting the usable search vocabulary for visitors to your site. Is this an effective way to build traffic? Absolutely not. Even the long tail of keyword research is restrictive: but, rather than favoring a very small vocabulary it opens the doors to cover your topic as thoroughly as you can imagine.
Open your mind to all of the possibilities: consider that people’s vocabulary choices are based on their life experiences, not yours. No short list of keywords can possibly encompass the search terms used by your visitors: even when attempting to apply a list of thousands of terms across your site, you can safely gamble that a significant portion of your visitors may still arrive via terms you have not considered. All you can hope to do is make certain that the broadest scope of descriptive terms for your site are present and available to be indexed and searched.
And, of course, there is a corollary advantage to wide-ranging keyword research: you can expand your own vocabulary in the process! 🙂