In the 101126 MMD Thijs Haenen wrote:

    "A roll system might complicate things a little, as you wouldn't be
    able to quickly select and switch out each tune, according to the
    demands of the audience".

Books, just like rolls, are played from the beginning to the end: from
the beginning of the musical piece (waltz, foxtrot, etc.) to the end.
As we could see on the embedded videos, the organ is playing books,
each book containing just one dance.  And a book, when ended, is quick
and easy to follow with another one, placed by hand. I think placing a
new book this way is indeed quicker then putting on a new roll.  But I
don't really know how quickly rolls can be changed.

Jan Kijlstra