If the latter, pg makes a good argument in section 4.8 of On Lisp:
"So yes, reading a bottom-up program requires one to understand all the new operators defined by the author. But this will nearly always be less work than having to understand all the code that would have been required without them.
If people complain that using utilities makes your code hard to read, they probably don’t realize what the code would look like if you hadn’t used them. Bottom-up programming makes what would otherwise be a large program look like a small, simple one. This can give the impression that the program doesn't do much, and should therefore be easy to read. When inexperienced readers look closer and find that this isn’t so, they react with dismay."