Nice post Phil - [url]http://www.addiscombe.org/joy-time-trialling/[/url]
As Phil mentions briefly there is a lot involved for the organiser in putting on these events and it starts a long time before the race, it is for this reason that people stepping forward to offer their help early is a massive help. In the build up the couple of weeks before the organiser has to collate all entries, seed the field, prepare a startsheet, send that out to all riders, helpers, timekeepers and so on, and then they have to prepare for the big day itself getting all the signs ready etc.
If they know before this time that all marshal spots etc are filled then it allows them to concentrate on the event itself and is a huge weight off their shoulders. Same applies for road races, cyclo-cross and the other Addiscombe promotions.