In the late 1990’s, Frames were sometimes used to hijack pages from other websites. This was considered unethical. It was essentially stealing content and rebranding it. I’m not an advocate of this HTML Frame con.
I am fan of embedding a web service into a Frame. These services include such things as: Blogger, Jalbum, form processors, and other “cloud or widget” resources. More seem to come into existence every day. They are modules or patterns. The feeling is you have never left the main site.