There you've been, snaking extension cords in the dark from your appliances to the generator outdoors.
Some folks go so far as to hot-wire their furnace to the generator.
When power is restored, if current from two sources suddenly surges through wires, the result could be serious damage. A special electrical panel is a safer solution. An electrician should install these, which can double the price. Still, either is a good investment. These panels work something like the circuit-breaker box in your home.