The 20 amp circuit breaker with 12/2 cable and 15 amp duplex receptacles allows for a total sustainable power consumption of 1,920 watts (20 amp x 80% x 120 volts) as opposed to 1,440 watts (15 amp x 80% x 120 volts). Thus, the 20 amp circuit breaker allows me to run a 1,500 watt spacer heater, a 170 watt laptop power adapter, and 2 external monitors all on the same circuit, which would NOT be sustainable with a 15 amp circuit breaker under the 80% load rule.