Intentionally blank pages are usually the result of printing conventions and techniques. Chapters conventionally start on an odd-numbered page; therefore, if the preceding chapter happens to have an odd number of pages, a blank page is inserted at the end. Book pages are often printed on large sheets because of technical and financial considerations. Thus, a group of 8, 16, or 32 consecutive pages will be printed on a single sheet in such a way that when the sheet is mechanically folded and cut, the pages will be in the correct order for binding. Such a group is called a section or signature. Books printed in this manner will always have as many pages as a multiple of the large sheets they were printed on, such as a multiple of 8, 16, or 32. As a result, these books will usually have pages left blank.
For example, if a book with 318 pages of content is printed using 32-page signatures, it will require 10 signatures, 320 pages in total. At the very end of the book — that is, at the end of the last signature — there will be 2 unused (blank) pages.
If a printer's document processor has been designed to skip completely blank pages, notices may also be required on intentionally blank pages to prevent incorrect page numbering.
Intentionally blank pages are ubiquitous in technical and instructional manuals, directories, and other large, mass-produced volumes of text. The contents of manuals produced by a given product's vendor are often compiled from generic instructions suitable for a variety of products, with additional instructions or chapters included for the specific product or model in question. This automation of manual-generation leads to intentionally blank pages required to fit the requirements for mass printing.
In digital documents, pages are intentionally left blank so that the document can be printed correctly in double-sided format, rather than have new chapters start on the backs of pages. Intentionally blank pages have also been used in documents distributed in ring binders. The intention is to leave room for expansion without breaking the document's page numbering. This allows updates to be made to a document while requiring minimal new pages, reducing printing costs. The only drawback is the increased time required by the reader to manually insert various newly updated pages into their correct locations in the document.
Intentionally blank pages can be useful in standardized tests such as the GCSE, Higher School Certificate, SAT, CAT, ACT, MCAT, and GRE. In these exams, there are often individual, timed sections in which test-takers are prohibited from proceeding to the next section until that section's time interval has passed and the examiner allows them to continue. Because all of these separate sections are printed consecutively in the examination booklet, it may be possible for a test-taker who has finished the section early to see through the page and read the problems in the next section. By placing intentionally blank pages between these sections, the test-taker is prevented from cheating in this way. By printing a notice on the page, such as "this page has been intentionally left blank", test-takers will not be concerned that their test has been misprinted.
I copy pasta'd Wikipedia to be a buzzkill.
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