Was looking around on a Delta itinerary at the "special service requests" at the bottom. If you check the box to notify Delta of a peanut allergy, not only do you prevent peanuts being served to anyone on the flight, you have the option to pre-board:'
When notified, Delta will not serve peanuts or peanut products onboard your flight. Cabin service will board with non-peanut snack options. Gate agents will be notified in case you'd like to pre-board and clean your seating area. Unfortunately, we still can't guarantee that the flight will be completely peanut-free.
I suppose the early boarding allows people with peanut allergies and their service animals to settle in nicely.