Switches are electromechanical devices. The are used to control the path of current or energy flow. Power switches are used to turn on and off loads. The contacts should be robust and have immunity to sparking and corrosion. Switches for signals need to be gold plated for low contact resistance and within a sealed enclosure.
Illuminated Rocker and Plain Rocker DPDT switches are popular in Power Boards and Extension Boxes for Mains power switching. Both Phase and Neutral lines are switched ON or OFF. This is not only safe but also reduces sparking.
Toggle Switches with metal levers are used in signal switching and range selection. Some may be switching Low DC or AC Levels less than 5V and currents in uA.
Pushbutton and Tact switches are common in circuits with digital controls. Tact is for signal switching. Large pushbutton switches are used in control panels for Motor and Heater Control.
A Neon bulb should have a resistor is series to make a Neon Lamp. All specs in designer viewpoint.
Switch contacts and fuse contacts can spark badly and cause fire hazards, periodic examination, service and replacement may be necessary. The sparking also causes spikes, emi, along with inductors or coils or even long wires that are wound up in the path of current. This effect damages smps and electronic systems in its path, if not adequately protected.
The low signal switches do not have the above problem. Then.. switches that need to control microamps of current and battery contacts of portable electronics that consume micro power have a unique problem. A thin oxide layer on the contacts or thermometric emfs due to electroplating defects can cause bizarre effects. These contacts must be immune form the environment, sealed, gold plated and clean. Even a little ammonia gets close to the contacts could cause problems in signal and power switches.
Water, sunlight, corrosive fluids and exposed or heating electromechanical contacts in connectors and switches are a designer and service engineering challenge.
Nickle Silver Alloys are used in some contacts of switches, relays and connectors. Beryllium Copper is used for its Spring action.