It's quite common for nonprofit organization to rely on event‐based volunteers for simple tasks like helping prep the facility, staffing the door, cleaning up afterwards or even doing more skilled work like working audio/visual equipment. The problem is, sometimes, these supports are of the “one‐and‐done variety”—meaning, they don't stick around in the weeks and months afterward to continue their support for your organization. They do their part in a limited capacity, plugging themselves in when it is convenient for them, without having to make a distinct time commitment.
A Wed, study studied this question.