With an electronic version of a loose - leaf there is no need to file materials and there are no problems with missing pages. (slaw.ca)
Having an ebook which is missing page numbers looks very unprofessional, and almost puts a red flag up to readers that you're new at this. (artfulpublications.com)
You'll see a Flash - based preview of your book, which is almost useless except for checking gross errors like missing page breaks. (johnaugust.com)