Using a frameset when designing a website can often be a bad idea, since it can really hinder your ability to create effective search engine optimization. The problem with frameset pages is that they cut into your ability to link all over the site, since generally the pages don't change, and links are accessible form one space. Not being able to link to individual pages can really hurt your SEO link structure, which in turn can hurt your link popularity and Page Rank rating, which is a huge part of SEO marketing. The website can have only one URL that can be linked to, which is that of the frameset index page. Homepage links make for less valuable links in link popularity strategy, so this can be a huge barrier.
The other major problem with using a frameset is that many search engine crawlers are unable to follow the frame sources from the frameset page, and thus are unable to access the content within them. When crawlers visit your index page, they won't be able to follow the frameset, and instead will probably only get a text explaining that their browser doesn't support frames, at which point they won't even bother scanning your site, which means your site won't get ranked.
However, if web optimizers can provide links to the main content pages in the No Frameset text, the crawlers will be able to follow them and find your actual content and analyze it for keywords and relevancy. The problem here, however, is that if these are the pages that are ranked and displayed in search engine results, they will be totally out of context with the frameset structure of the site. This will prove quite confusing, and could cause you to lose a lot of visitors.
In general, Framesets aren't the best option if you're looking to nail your search engine marketing strategy. They eliminate the use of a lot of SEO tools since you are essentially displaying multiple pages of content in one setting, losing the ability to link and making keyword separation harder to decipher for crawlers. In the end, you're going to attract more users and traffic from search engines than by having a fancy frameset page. Keep away from the use of frameset if you can.