A vocal lead marks who sings what on each section; vocalists and leaders see the tags. On the Plus and Pro plans.
Vocal parts are on the Plus and Pro plans.
Anyone tagged Vocal Lead (plus leaders and admins) can mark up vocal parts.
Open Vocal parts from the sidebar to manage the church's list of labels (Melody, High harmony, Descant…), or tap a section heading on a chart to set that section's parts. Each occurrence is separate — the first Chorus and the second Chorus can carry different parts.
The badges only show to vocalists and leaders, so instrumentalists aren't cluttered with them. Every change records who made it.