When using the job signup tool in VSys Live, if a job slot allows one or more self-waitlisted volunteers, VSys Live will allow more people to sign up than the slot actually needs. Why? You:
Volunteers who self-waitlist get assignments with the status of "Waitlisted" or "Waitlisted and pending release form" depending on whether the volunteer requires a release form for this job or not. She will get a Waitlist position as well, indicating her order in the list (lower-numbered volunteers signed up earlier). You can then use the Job slots and assignments into them tool to manage your waitlisted volunteers.
To enable slot waitlists, use VSys Live -> VSys Live Sites and Settings -> Advanced feature enabling and check Enable job waitlists.