visa applications and number of empty pages in passport

when applying for various visas, I think I hv seen requirements such as 'there would be X number of empty pages' left on the passport/TD etc.

is that a legal requirement? or just an operational requirement.

asking bcoz I am running our visa pages in my passport and not sure if it be a problem for me soon.

thanks

Different countries have different requirements.

If a visa sticker is issued. then definitely at least 1 blank (some countries ask for 2) page is needed. Get a replacement if running low on pages

thanks both. if 1 pages is required, I can understand (needed for the sticker), why demand 2? this is what I do not get...

Maybe so they can put entry stamps/etc at the border on a second page so they can be read clearly.