A continuous feed garbage disposer runs only when it is manually switched on. The switch can be a regular wall switch or a counter top "air switch" (a non-electrical switch safe for wet environments). The disposer is operated by turning on the cold water, switching on the disposer and dropping kitchen debris into the drain hole in the sink. After the debris has been thoroughly ground up, turn off the disposer and then a few seconds later turn off the water.
The main advantage of a continuous feed disposer over a batch feed model is that you can continuously to feed in garbage until you are done. This is simpler and more efficient than a batch feed model.
The key disadvantage of this model is that it is more dangerous. It is possible to turn it on while reaching into the drain. Because the drain is open during use, there is also a risk of things like silverware, falling in while it is operating.