Narrow DOF portraits are terrible with one eye in focus and the other not. People are caught up with the capabilities of the technology rather than the aesthetics of what they should produce. Head should all be in focus. Back in the old days, (am I really that old?), big fast lenses with large openings were often required because film was slow. Not so much a problem today with high ISO's. Also, the other advantage with large glass lens is that they transmit more light before the aperture closes down. That makes it easier to see the subject in reduced light and focus better (manually, of course back in the old days). With AF and now digital viewfinders, that's not necessary. But people are willing to spend whatever and shoot likewise because they think it makes them better photogs or at least more important. Me? I shoot landscape mainly so I like little openings for DOF. I also bracket because I don't trust myself. (Gosh I am getting old!)