The "This ministry may be scheduled in combination with..." setting allows you to specify that the same person may be scheduled for two ministries at the same service. This setting is easy to understand intuitively but the specific behavior is a little complex, which is why we have this special article explaining how it works! There are three variants of this setting that behave slightly differently.
ONLY WHEN NEEDED
When this setting is set to "Only when needed" it will only schedule the same person for two ministries if there are not any other volunteers available for the second role.
When the "schedule in combination with" setting for Ministry A is set to "WHENEVER POSSIBLE" with Ministry B, a volunteer can't be scheduled in an empty Ministry A position at a service unless 1) they are qualified for and can also be scheduled in Ministry B, or 2) there are more empty positions in Ministry A than in Ministry B. So, for example, if a volunteer is just qualified as a Gift Bearer and not an EM Host and there is just one open position in both ministries, then the volunteer can not be scheduled as a Gift Bearer at that service. However, if there were two open Gift Bearer positions, then the volunteer could be scheduled in one of those empty positions.
The only exception to this rule is if the volunteer is 1) not qualified for Ministry B and 2) the total number of positions (empty + filled) required in Ministry B at the service is greater than the total number of positions in Ministry A. For example, if a volunteer is just qualified as a Sacristan and not an EM and there is only one Sacristan position required total at the service but four EMs, then the volunteer can be scheduled in an empty Sacristan position at that service (even if all the EM position have already been filled).
The "ALWAYS" setting is similar to the "WHENEVER POSSIBLE" setting, but more strict. When the "schedule in combination with" setting for Ministry A is set to "ALWAYS" with Ministry B, all of the requirements for "WHENEVER POSSIBLE" must be met in order for the volunteer to be scheduled. In addition, if a volunteer is qualified for both Ministry A and Ministry B, then he MUST be scheduled in both ministries whenever he is scheduled for the other. For example, if a volunteer is qualified as both an EM and Lector, and there are four open EM positions and no open Lector positions, the volunteer could not be scheduled as an EM, since there is no room for him to be scheduled as a Lector at that same service.