I don’t need an aeration system, I have a waterfall.
Waterfalls are extremely effective as sources of oxygen for your fish. But if your waterfall stops, your oxygen production stops.
An aeration system is really like a spare tire. You don’t really realize the value of it until you need it. If your pump is going to go out. It will likely be right before a 3 day weekend when everything is closed or when you have someone watching the house that isn’t very mechanically inclined.
Air Pumps require quite a bit less electricity and are easy to run off of a battery backup or small generator in an emergency situation.
A secondary air source has many other benefits other than just being a secondary air source in an emergency. It helps to circulate the water by bringing what is down at the bottom up to the surface. The extra oxygen can also help with the overall health of your fish. It does disturb the surface so put the air pump on a switch that you can easily turn off when out viewing the fish.