One drawback of charging on an 120v (or 230v) outlet is efficiency. While charging, the energy consumption of an electric car can easily reach 300-400 watts. When you're only charging with 1800-2400 watts, that's a sizeable amount of energy that never reaches the battery.
With a dedicated level 2 charger, you can charge with 10+ kW, making the percentage that is lost in the electronics of the vehicle much smaller.
With a dedicated level 2 charger, you can charge with 10+ kW, making the percentage that is lost in the electronics of the vehicle much smaller.