A toggle is a simple user interface control that allows users to change a setting between two opposing states. When used correctly, toggles can be a good alternative to checkboxes and radio buttons. They are especially useful on mobile devices where space is limited and a toggle can offer immediate results without the need for a separate Save or Confirm button. However, they should only be used when the choice is between two opposing states (for example, toggles work well for changing Airplane Mode). For less clear-cut cases, a radio button might be better.
As a design pattern, toggles can cause cognitive problems when they are not carefully implemented. For example, a toggle switch that looks like a slider and uses colors to convey state can confuse users who haven’t read the associated text. Designers sometimes try to mitigate this by adding text that describes what the current state means, but that can be difficult to do well. For instance, using a red-green color scheme for toggles can be confusing for some users with color vision deficiency since they will only see green when the toggle is turned on and red when it’s off.
Additionally, many teams use toggles as a way to perform multivariate or A/B testing. By defining a toggle with an experimental flag that sends users down one codepath or another at runtime, it is possible to test whether different versions of the same functionality have similar or differing impact on user behavior. This is a common technique that can be quite powerful when used properly, but it can also introduce unnecessary complexity to an application and may require a significant investment of time to set up and manage a toggle configuration system. To make things easier, savvy teams try to keep their feature flag inventory low and remove toggles that are no longer needed as soon as they can.