I do a lot of DD, and I'd bet that 75%+ of my restaurant orders are a single order going to a single house. I prefer grocery delivery, and it's probably closer to 50% for those, as we often get a couple of orders at once.

Occasionally we get a single drop off with 2 stops (pick up food from a restaurant and something from a drug or grocery store, and drop them both off together).

I've never gotten more than 3 orders at once, and those are pretty rare.