For better readability of a conductor's score it's possible to show chord symbols only on selected staves.
For example if a jazz band score has chord symbols on the piano, electric guitar, electric bass and vocal staff, it make senses to limit their visibility to the piano and/or e-guitar staff. This will give you more vertical space on the page.
The Perfect Layout plugin offers to show the chords on all staves in the score, or on one or on two (Option: "Show Chords in Score Only on Staff
This only affects the score. In the parts all chord symbols will be visible.