“When circumstances require it, the pastoral care of a parish or of different parishes together can be entrusted to several priests in solidum, with the requirement, however, that in exercising pastoral care one of them must be the moderator, namely, the one who is to direct the joint action and to answer for it to the bishop.” (Wikipedia, ‘Team of priests in solidum’)
When a parish or church is closed, the attending priest has a dramatic change in daily responsibilities and the people for whom he works. If the relevant archdiocese is closing several churches or parishes, the priests who lose their holy jobs most likely will find themselves transferred to a team of priests who look after one or more parishes. This would be a major change in their vocation, and the authority for what they do will come from the “moderator.”