Hidden (or invisible or transparent) notes can be useful in preparing theory or composition exercises.
c4 d4
\hideNotes
e4 f4
\unHideNotes
g4 a
Hidden notes are also great for performing weird tricks. For example, slurs cannot be attached to rests or spacer rests, but you may with to include that in your score – string instruments use this notation when doing pizzicato to indicate that the note should ring for as long as possible.
\clef bass
<< {
c4^"pizz"( \hideNotes c)
\unHideNotes c( \hideNotes c)
} {
s4 r s r
} >>
This page is for LilyPond-2.4.5 (stable-branch).