Why are pages intentionally left blank?

One reason is so that pages can be inserted in later editions without requiring the renumbering and relabelling of the later parts of the book or report. Thus page references continue to be valid across editions.

I've seen this work. Sometimes.

Also:

https://www.google.com/search?q=Why+are+pages+intentionally+...

http://en.wikipedia.org/wiki/Intentionally_blank_page

Google is quite good at finding out things like this for you.

Well I don't know for sure but here are couple of reasons I can think of.

1. to make a new chapter/section always start on a facing page.

2. I used to work for a banking software firm and they provided very large paper manuals (several thousand pages) to their clients for the various systems. They would always leave blank pages scattered through the manual so they could ship paper corrections to the manuals without reprinting the whole thing. This allowed the page references in the later pages of the manual to remain correct. (This was 20 odd years ago, I'm sure their manuals are PDF now.)

The best set of answers I have seen.

http://www.quora.com/Why-do-books-sometimes-have-pages-marke...

what is paper?