The KCL Caterer makes you use his waiters, (he makes a few hundred on that). The caterers waiters will make sure to take care for his boss-if the fire goes out or too high or too low, or the urn needs adjusting or water added. He'll also protect his bosses equipment that it doesn't get lost, etc.
As they say "yom-tov in der vochen".
What's about "bossur-she'nisalem"? among many other issues.
Who controls the caterer's hot-box? (who has the key to the locked hot box? you guessed it, the Goy)
and his other equipment?
and the "party planners" putting their items in the warmer, oven etc.
All without a mashgiach, thanks KCL
Defining a "drop-off"-Any other reliable Hashgocha will only allow a "drop-off job" in a person's house, but not in a shul, hall, etc.