Different Number of Staves in a Song
The command Insert: Boundary Change gives the power to collapse staves (so the print could have 3 staves, 2 staves, 3 stave, etc) and add a gap to the staff.
The following files might assist in learning more about how boundary changes can be used.
This document shows examples of the command using included the following linked files.
Use a boundary change to combine two short songs onto a single printed page.
Use a boundary change to start with a single staff system, then show a second staff in the second printed system, then revert back to a single staff in the final system.
Use a boundary change to collapse a staff for one or more printed systems.