Firstly, the performance Robin Williams gives in Good Morning, Vietnam is of such a high caliber that it is difficult to describe. His quick wit and comedic genius are what make this movie so amazing, and the director Barry Levinson knows it. He uses the camera to heighten and draw attention to Williams's insane presence.
One example of this is during the scene where Williams's character Cronauer meets up with a regiment of soldiers stuck in the road. In the scene Cronauer entertains the soldiers and Williams proceeds to give a wild performace. Despite the unpredictability of the performance the camera never loses tack of Williams. We watch the majority of the scene from an over the shoulder shot. With a third of the frame take up by an out of focus soldier, serving to remind us who Cronauer is performing for. It makes us focus on Cronauer and the connection he is building with these men. Levinson easily could have done a wide or medium shot for this scene, but he didn't. He chose to go with a tighter shot that shows the audience every expression and wild contortion of Williams's performance. With this decision Levinson gave us a better understanding of the bond Cronauer was forming.
Likewise when Cronauer was having a breakdown on air, Levinsion moved the camera into an extreme close up. Beads of sweat could be seen dripping down Williams's face. The audience can only watch as Cronauer agonizes over what to do, becoming so distraught that he bangs his head against his microphone. Then when he finally gives in and shares the news of the bombing on air, he is cut off. Levinson pauses, and cuts to a wide shot where Willims is framed by a square window and seems strangely detached from the world around him. It makes him seem boxed in and contained by the world he is in. This shot makes expert use of Williams because it is so in contrast with how he normally is. The audience is so used to being close to Robin Williams's energetic performance, that when Levinson cuts to a wide shot, where Williams is dead silent, the impact on the audience is doubled.
These scenes give filmmakers a very important lesson, which is to use your framing to reflect your actor. Robin Williams is a wild personality and the audience wants to be drawn in and be focused on him. Levinson gives us what we want, and then later when the character is faced with emotional turmoil creates contrast by changing up his framing. If the framing of Williams was not so well done, then certain moments may still have been funny, but the emotional aspect of them would have been diluted. Filmmakers must remember who their actor is and use framing to best reflect that actor's energy.