Well, if you open a book you're currently reading you can pretty easily tell which parts you've already read and which you haven't - but you still probably use some sort of bookmark to avoid going through the hassle.
This sounds similar, a matter of convenience rather than a need. Glance at a bookshelf and you can know visually what's still unread without checking the books one by one.
This sounds similar, a matter of convenience rather than a need. Glance at a bookshelf and you can know visually what's still unread without checking the books one by one.