Using Frames are Bad for SEO
Frames are a major issue when it comes to SEO and can not only present problems with the search engines from spidering your site, they can also make it a navigational nightmare to navigate. Frames load your website as single page. This makes the search engines think that your content never changes and you only have one HTML page.
Frames are used by many web masters for navigation and layout to make the site easier for users. Frames will typically keep the top portion of the page stationary and when the user clicks on a link it will load another page in the window below or next to it. Search engines are not able to scan sites that use framesets because of the ability to move to different areas of the frame. If your site is using frames more than likely the search engines are not getting to your content.
While they are valid in terms of the HTML specifications, they offer very poor cross platform support making it difficult on mobile devices (tablets, cell phones) to view the page fully. In essence, when using framesets you are restricting the design of your website to the parameters of the frameset.
If frames need be used, a better alternative would be to use an <iframe>. An <iframe> (inline frame) is treated just another element on the page and can be adjusted like any other element with CSS which allows you to redesign your site without touching the HTML. The <iframe> is also a bit more search engine friendly as the element is embedded into a page so that you already have content surrounding it.