Footer backlinks have their place in SEO. They are powerful as long as they are on powerful websites. Most links are powerful if they came from powerful websites. On the other hand, for best results, they should only be in the footer of the home page. Footer links on websites with a lot of pages will give you thousands of backlinks from the same website and with the same anchor, which is a bad practice. Footer links are also way below the fold of the website and usually not contextual (inside an article). So a simple homepage backlink inside some text will always work better than a footer link. But if you can't get something else, footer links on powerful websites, in some particular cases, will work, of course.
