Toggle is a technique that allows us to perform multivariate or A/B testing. A given user is sent down one codepath or another based upon their membership in a cohort. The results of the experiment can then be analyzed to drive data-driven improvements to things like the purchase flow in an ecommerce system or the Call To Action wording on a button.
While a toggle is very powerful in the right hands it can be dangerous when used indiscriminately. This is why many teams move their toggle configuration away from static files and into some type of centralized repository where they can be more easily modified and verified at runtime. This can greatly reduce the risk of accidental feature flag changes by a team member and also speed up the process of validating new toggle configurations for a release by removing the need to re-deploy a service instance to test the effects of an override.
A toggle switch is an easy to use, powerful tool for managing a number of features simultaneously. But, when designing a toggle interface it is important to consider the two primary aspects of the control: visual signifiers and state descriptors. Good toggle switches should have clear, direct labels that make it easy to understand what option the toggle controls and what its current state is. Toggle switches should also utilize strong visual cues to ensure that users can see that the toggle is positioned in a certain position and not just by reading the label.