Mark Engblom has a very cool post up about Robin, and the seemingly endless ways he appeared on DC covers looking on and commenting as Batman performed some amazing feat. The on-looker in a 3/4 shot was an important part of making the panel or the cover seem three-dimensional. It gives us a close, recognizable person so we can gauge the relative size and nearness of everything else in the view. This is used endlessly throughout the Silver Age. Look at every panel on this page:
You can see that in every case there is somebody standing in one or the other bottom corner who is the closest to the "camera", thus giving us scale. But notice that they do not have always the same angle that they're looking at. In the first panel, a salesman is looking directly left. In the second, Lois is looking back and left. In the third, the professor is looking forward and left Then we see Lois looking right, then left, then the professor looking forward and left.
I tend to think of the camera angle where the person in the foreground is mostly facing away from us as the 3/4 shot, because the onlooker is 3/4 looking away from the camera. In this page the third and sixth panels are used this way. In the ones Mark has posted of Robin, I believe that if you look closely at them, you'll see that every one is a 3/4 shot. Granted Moldoff doesn't make this clear always until you look at the set of the shoulders.
Now, here's the thing. The world's worst comics artist at drawing the 3/4 shot has to have been Wayne Boring, one of the major Superman artists of the Silver Age of Comics. And the main reason why was because he just could not place the eyeglasses on a character to save his life.
We have two examples right on the page I posted above:
You can see the problem, right? The angle is all wrong on the glasses; they look like they're about to fall off his nose, rather than balanced on the bridge. This is a major artist, on a major character who often wore glasses (as Clark Kent), and the artist just couldn't get it right:
And it went on for years. We all bow down before Weissinger, who undeniably created an amazing decade for Superman, but how do you ignore the fact that he let this travesty go on with the glasses?
It's not as if DC didn't know where to put the glasses; Al Plastino knew where they belonged:
Boring was a terrific artist in the Golden Age, and I would not have been able to draw anywhere near as well as he did on his worst days. But he almost never got the glasses right.