I've had occasion to typeset extraordinarily large matrices, which I didn't seriously expect anyone to expect in detail (without a computer) or print, but I needed it to be obvious that they were completely explicit and written down somewhere.
By trial and error, I found a really large paper size that would compile (about 5.5m) in pdflatex and fit my matrices on a reasonable number of sheets. (I used the geometry package to choose custom page sizes.) But it would have been easier if I'd been able to find out:
What are the limitations on paper sizes in pdflatex?