Walkup check in jobs are a special type of job applicable only to the VSys Kiosk and optionally VSys Live. They are jobs which volunteers can check in for without having a pre-defined assignment. Volunteers are still subject to the job requirements defined as part of the job itself. For example, if the volunteer does not have a required skill for the job, he will not be allowed to check in for it.
Use this to allow a large number of volunteers to check in for a special event or project without creating a job association or assignment for each and every volunteer. This can be useful when you have invited a number of people, but aren't sure who exactly will be showing up.
Walkup checkin jobs are specific to the site under which they're created.