This question is quite general. Nonetheless I believe that it touches upon something fundamental. That said, anyone feel free to improve the question.
LaTeX can be thought of as a complex algorithm that does everything without manual fine-tuning. In most cases, one needs to run LaTeX just twice, which is remarkable given that it is a linear compilation process. However LaTeX's design also leads to the disadvantage that certain types of fine-tuning which conceptually really are best done during a post-compilation phase are not easily done with LaTeX.
An example: say I would like to remove the page numbers of all pages with a figure at the top of the page. (If you can think of a better example, feel free to improve the question.) What are ways in LaTeX to make such post-compilation changes easiest? (The idea is that the user can supply additional data after "compilation proper", and one would then run a post-compiler that does some minor fine-tuning.)
I understand that the right answer wouldn't be "a single LaTeX command". Instead, answers might point to (La)TeX derivatives, constructions or tricks on top of the standard LaTeX engine, or conceptual pointers. (And, yes, of course solving this problem will require one additional compilation pass at the end, either directly by LaTeX or by something else. I suppose one could do the initial compilation phase(s) by "something else" and the final run by LaTeX proper. This is an open question, and creativity is welcome.)