There is no savings to cancel a flight because of load (unless cancelled months in advance before there are many bookings). The airline still has to pay all other costs (flight crew, lease on the airplane, lease on the gates, flight dispatcher, mechanics), plus the aircraft is now out of position in it's line of flying. What does happen, is if there is a busted airplane, or lack of crew, the airline will try to affect the fewest number of passengers and connections. Many airlines use sophisticated automation to help them in these decisions.
Rough weather day on the east coast, so not much can be done other than reduce the schedule to try and keep what you can fly intact. Most "ATC fragile" airports are unfortunately scheduled at near or at their VFR good weather limits (runway and airspace capacity).