Another use for visuals is at an airport with parallel runways which are too close together for simultaneous ILS's. So one gets the ILS, the other the visual. The way to do this is to vector one a/c all the way onto final keeping vertical with the parallel traffic, then issuing the visual approach , thus ensuring exact positioning of the a/c, which avoids said a/c turning base wherever they see fit, as was mentioned earlier. (this is the 'Reader's Digest' version of what we actually do...)