As the name suggests, a footswitch is any of a number of different types of switches operated by the feet. It can either work in a simple binary manner, with only an on and off setting, or it can work on an increasing scale. The one that most adults are familiar with is the gas pedal of a car.
In any operation in which both hands need to be used, a footswitch is a perfect way to add greater control. While driving a car, your hands are used to steer, shift gears, operate the radio, and if you're bad like most of us, use your cell phone and drink your coffee. Having a foot pedal to control the acceleration and breaking allows you to use your hands for other tasks.
Freedom to use both hands on a project is useful or vital in many artistic and manufacturing processes. Many types of cutting and shaping tools use a footswitch as a clutch or speed control. Since both hands are needed for the safety of the operator, especially when dealing with heavy machinery, a this allows for maximum control.
In industrial settings, a footswitch can also act as a failsafe. In this case, it is also a "dead man's switch", meaning that if the operator is away from the controls for any reason, the machine stops. This helps prevent accidents that might be caused by a distracted or drowsy operator. A footswitch will also stop a machine if the person operating it is pulled away from their post by being caught up in the machinery.
Artistic activities often include the use of both hands, so a footswitch can often come in handy here as well. Guitar and bass players use can use a single one or an entire board of them to change the sound of their instrument, or to control their gear. Pianos and organs use pedals, which are also types of footswitches.
Potters who use a wheel can control its speed with a footswitch, leaving both hands free to shape the clay. Electrical sewing machines use one to control the speed of the needle, but even older manual models use a version that the operator powers by pushing. From industrial machines to musical instruments, whether for safety, control, or ease of use, footswitches are found in unexpected places throughout our day to day lives. If you look around, you'll be surprised at how many different things have such a switch attached.