They can range from having a staff of hundreds during the event to a staff of two in the early planning stages of the event project life cycle. The Australia Day event in Darling Harbour last year was organised by Accolade with a standing staff of two. As the day approached, they hired staff as required. When the event finished the staff went back to two. The event companies are organised along classical project management lines.
Correct delegation is their key to success.
They are only interested in outcomes and deliverables. The process is unimportant as long as the product works. Also there can be no second chances. This means that any product supplied must satisfy the conditions of the contract. There can be no refinement of the product on site.