You can only bookmark the home page of a Web site that consists of frames. You cannot link to a framed page. It's not possible to correctly link to a page within frames. If you do link to it, anybody following the link will miss out on the other frames such as navigation controls. Framed sites are more difficult for text-based and speech browsers.
Inexperienced designers can make all sorts of mistakes with frames.
One of the most common uses of frames is to show the effect of rows and columns. You can achieve the same effect with tables. In fact, tables do this job better. Another common problem is jamming lots of little frames onto the page. More than two or three frames creates a very cluttered page.