1.To include synonyms of words that are not included in the content of your page. People search on many variations of words and phrases. Sometimes it is hard to include all of the different variations of those words in the content of your page without making your page sound like a keywords page.
2. To place emphasis on certain words. It is not always easy to place your major keywords at the top of your page or in a
tag. Your major keywords might not be introduced until the middle of your page. Using the keywords meta tag, you can add these keywords to inform the search engines that these words are important. Remember two important rules when using this tag: When emphasizing keywords, do not place the same keyword more than two times in the keywords meta tag. This could be considered keyword spamming and can reduce your ranking value. Also, do not place irrelevant keywords in your meta tag. Using irrelevant keywords could get your site band from many search engines.
3. Another use for the keywords meta tag is to add words from different languages. A multi-language site with one language as its default page might want to add words from other languages to attract people speaking languages that are different than the language of the default page.