Why do we see "page intentionally left blank" so often in aviation related documents?
I've worked as a technical writer on flight and maintenance manuals in a previous life.  It's done with technical publications where there is a kind of quasi-legal status you might say, insofar as the information published is required for operation or maintenance, is invalid for use if not up to date, and where pages are revised, numbered and dated with a List of Effective Pages (LOEP) that goes at the front, that confirms the issue date of each page.  

It provides a ready confirmation that a blank page is not a misprint (even as a PDF or other electronic format), saving the reader from having to check against the LOEP to make sure there isn't a missing page every time a blank page appears at the end of a section.