Why 'Flat is better than nested'
 

>>> import this

prints 'The Zen of Python', a poem by Tim Peters that consists of python
proverbs such as "Flat is better than nested." (Others things being
equal) why? Because it is a restatement of the principle of parsimony,
of not multiplying entities without necessity.

Suppose we have a unstructured collection of N items. Organizer comes
along and says 'Let there be structure. Let us organize the items as
leaf nodes in a hierarchical tree' (which is equivalent to nesting). To
do so, we can add as many as N-1 new non-leaf nodes and as many as
(about) 2*N - log2(N) parent child relationships. In other words, nearly
quadruple the number of entities to learn, discuss, and remember. Well,
there had better be a good necessity to do so ;-).

And, of course, once new entities *are* conjured up, it is hard to get
rid of them.

--
Terry Jan Reedy