For example, if I have 'Soloist' as a volunteer Department, it would be nice to assign that soloist to that particular part of the service.
Or, if our case, we have a praise band that plays two modern worship songs during our service, and an organist that plays two hymns during the same service. It would be nice to assign the organist just to the 2 songs, out of the four, and do the same for the praise band.