Needing multiple pages is not a big issue if you always know what is where - but I agree it is suboptimal when a candidate starts moving things paper around and gets lost due to too many pages.
Here is how I set up my page:
1. At the top of the page, I write the question
2. Right below, I draw out my framework
3. Below still, I do my calculations & write down my significant findings (which I put in a box to quickly find them at the end if needed)
4. On the side, I draw a line ~1 inch away from the edge; at the top of that long rectangle, I write out a couple of words for each interim conclusion I have (useful at BCG if the interviewer doesn't leave me any time to prepare a final recommendation
5. At the bottom of that rectangle, I'll write down crazy ideas I have in the middle of the case but that aren't relevant just at that moment. That will help me not forget, and perhaps use in the 'conclusion / next steps' if I haven't addressed by then
Some people write a lot, or write big. If so, a 2nd page can be useful for the question + recommendation; a 3rd page can also be used for all the math. I think that's probably the maximum number of page most people can properly use in a case; anymore and you will stress yourself out while trying to find what you are looking for.
Hope this helps; good luck!