If you burn the gas in a power plant you turn something like 40% into electricity. You can deliver something like half of the remaining Joules as heat to homes, raising the overall efficiency to 60% or so. You can then use the 40% you have as electricity to run heat pumps, which put out something like 2-5 Joules of heat per Joule of electricity. In total this gives you a lot more Joules of heat per unit of gas than just burning the gas in the homes directly.