Events that are Sanctioned by PSOs, the NSO or the UCI (Union Cycliste Internationale) itself will have UCI Commissaires present. This adds another layer of complexity to cycling races, as rather than dealing with single organizer, you may have to deal with up to three different groups; the event organizer, the commissaires, and the sport governing body.
For the most part, the event organizer will be responsible for the logistics and setup of the event, such as determining the course, location of start and finish, and the daily schedule, while the commissaires will run the actual race. Many of the onsite decisions will be made by the commissaires, and they will do their own manual timing separate of yours, which they will use to confirm official results.
Commissaires can be a great help, and having a good working relationship with them can be the difference between a successful event and a terrible one. At the end of the day it is their event, and they can make changes and decisions you might not agree with. The easier time you have working the them the easier your life will be.