In Willy Wonka and the Chocolate Factory (1971), everything in Wonka's office is cut in half: half a desk, half a sink, half a safe, half a bust, etc.
Why is this?
That's pretty much all there is to it. It was a very simple and obvious way of bringing out his whimsicality and eccentricity visually.
The director, Mel Stuart, answered this in his book Pure Imagination: The Making of Willy Wonka and the Chocolate Factory, where he said:
the reason everything in Willy's office is cut in half was because Stuart couldn't bear the thought of - after having gone through all the whimsical and creative rooms in the factory - ending the movie in an ordinary office. Everything was cut in half to make the room look more Wonka-esque.
Both Alice in Wonderland, and Charlie in the Chocolate Factory, are examples of the trope of an ordinary child whisked into a fantastic world and shown incredible things. Perhaps this is the film's way of tipping the Wonka top hat to an older film adaptation of an older story with a similar theme.
During the construction of Willy's office, in which everything is cut in half, one of the prop men accidentally sawed in half a non-prop coffee pot that someone had put in the work area. Only when coffee began spilling out did he realize his mistake.