The Tour de Oz race on Friday had a Cat A and Cat C category. All 200+ riders started at the same time. It was difficult to determine if one was closer to the front, who the A and C riders were. In the outdoor races I have participated in with multiple categories, they would always send the faster category off first with a few minute lead. That way everyone in the second wave knew they were in the same Cat. Thanks.
This idea has merit.
Having only ridden in 5 races, and being a true class D racer, I have already figured out that my best race strategy is to bust it out of the gate and try to latch onto the wheel of a group with C riders (sometimes even a B or two in there). I can in no way ride at the front of this group, but normally I can hang onto the back for most of the race. That is just good racing strategy, but it would be better to be in a true group of D racers and be rotating to the front to carry my fair share of the load.
Having only a 15 or 30 second gap between groups would prevent guys like me from siphoning off the back of an upper class group.
The even bigger benefit is that such a stagger start would greatly discourage riders from artificially signing up in classes below their capability. If you are a C rider and register as a D, you are not likely to catch up with the higher classification riders. i.e. you will want to get in the group you can ride with.
For riders like me, you can readily see who you are competing with and begin to set up alliances and drafting strategies to pull your group towards the finish.