It does a lot of good IMO. If the flight still goes 12 hours late, you at least get to your destination (or at the very least to a hub). That's a lot better than having all the passengers on the flight scramble to grab the limited number of seats for the next day's flight(s) that haven't sold yet.

I recently had a 4.5 hour delay on a DL flight to ATL. I missed my connection that night, but I got home on the first flight the next morning. Some passengers did choose to just get rebooked the next morning, but 1) the seats on the morning flights to ATL/DTW/MSP got snapped up quickly, and 2)most people who had to connect wouldn't get in until early afternoon at best. I was glad the flight went in order to minimize delays. This particular flight was from a domestic location with flights to 6 cities that are all at least focus cities, but the cancellation vs delay value proposition would become even more drastic if we were talking about a destination with only once- or twice-daily service (e.g., many international locations that aren't partner hubs or cities like ELP that see 2x daily flights to ATL and nothing else).