It's also pretty useless. (Wow, am I cranky today!)
A previous visualization of Title 11 at least color-codes different sections of the title so you could get some feel for what portion of the law was dedicated to Chapter 11. The post there states:
Much of my training in law school (particularly in the so called “code-based” classes) was focused upon developing mental models for the structure and content of graphs such as the one displayed above. In my case, I believe the usage of such a visualization early in a code-based course would have been beneficial. Thus, we offer this traversable visualization to the world for not only its research value but also for pedagogical purposes.
I can imagine that if I'm studying to be a lawyer, I need some mental model of how the law is structured. Their claim seems to be that the visual tree representation could help, presumably by allowing a visual thinker to recall a position in the picture even if he or she could not immediately recall the index of the desired paragraph.
The picture may be useful for counting off various elements (another shade on the pedagogical use), or for observing the differences in depth between different sections, or (with some effort) estimating the size of different sections. I might even buy it as a rhetorical aid illustrating the "complexity" of the tax code.
But as a visualization I feel like it's just one 'axis'. It would be much more interesting to combine with a different data set, such as highlighting particular keywords within the structure or looking at rate of change. A picture of a tree by itself doesn't give much to work with. I don't think Tufte would have good things to say about this graph.