Cathi Vought found this gem in a report of the typhoon response in the Phillipines, "The Yolanda Tragedy: 7 Lessons in Early Emergency Response". Volunteers were used by the local police to stretch their forces and keep order. The following quote is from roughly half-way through the article:

While sipping coffee with some of the policemen, two officers and a local businessman who owns a nearby warehouse came. The officers organized an eight-man team to secure a wealthy enclave of Tacloban. The businessman told us four of the five suppliers of prime commodities in the city had already gone and were not coming back any time soon. The biggest rice miller, he said, would also be leaving the following day. His story strengthened my resolve to pull out my family as soon as I could reach them.
What set me thinking, though, was the judiciousness of deploying eight policemen to secure the houses of the rich. If that pattern of deployment would continue, I thought, they won’t max out the services of the 30-man contingent. Lesson No. 5: Security managers should exercise prudence in the deployment of limited forces. In communities not badly affected by the disaster, unarmed multipliers perhaps can be organized to protect their own communities freeing up more policemen and soldiers to lead in recovery, maintain law and order, and guard crucial establishments.

The corrolary to this, is that potential volunteers need to be trained in how to communicate efficiently and effectively with the police. Volunteers are not Law Enforcement, which means that if they get in over their heads, they need to be able to call for help from the professionals, get it quickly, and coordinate effectively with the police who respond. That takes training, preparation, and exercise before disaster strikes. But if that coordination does happen, a tactical reserve of police can be employed where and when they need to be, maximizing use of a limited resource.