I did this twice:

1. I was very drunk and had Dairy Queen delivered. I was immediately ashamed when I saw the bill and hid all the evidence from my wife in shame. Would not recommend. It was over twice the cost.
2. I was in a rush for a trip, the car had issues so I needed to get a rental the morning of, and I didn't have time for breakfast or to stop at a fast food restaurant. So I made the horrible choice of getting junk food delivered while I got ready. Overall not a horrible choice, but I wouldn't recommend it.

The economics of delivering fast food are awful.