I've always thought it would be useful to see a listing of all destinations reachable by either non-stop or direct (one or multi-stop) flights from my point of origin. Some people do not like to change planes, perhaps due to limited mobility or ???, and might be opportunistic enough to be willing to fly on vacation anywhere a non-stop or a direct (single aircraft) flight would take them.

e.g. I live in YYZ but often use Southwest from BUF. I prefer non-stop flights so when I go to FL I would be willing to fly to any of Southwest's FL destinations, PROVIDED the flight is non-stop.