I agree, gains should go to reading the code most of the time. But when you say

> It is a suspect proposition that anything is gained by turning 3 lines of code into one line of code.

Some code is way more verbose than its description would be. A named function signals intent:

  function multidimensional_transform(the_data)

And for Javascript ES2015 there is new syntax (like spread operators) that improves code the same way.