One of the problems of using manual focus lenses on Canon EOS bodies is that focus confirmation is disabled. When AF lenses are used – even in manual focus mode – all Canon EOS bodies confirm focus with a green dot in the viewfinder and an (optional) audible beep. However when non-EF compatible lenses are used via an adapter, the focus confirmation is disabled. Unless the camera thinks that an EF compatible lens is attached to it, it switches off both visual and audible focus indication.
Focus confirmation chips ‘trick’ the Canon EOS body into thinking an EF lens was attached, so that the focus confirmation indicators work with any lens attached.