When developing a new feature for a mive-store. Ideally perform it in on a dev-store/environment until it is finalized & ready for implementation. Then once it is read for implementation, it may take updating several page-templates, global-templates, and other misc. places in order to activate the new feature.
To test the new-feature on the live-store in a seamless & safe manor we can prepare all the changes underneath a series of conditionals that will evaluate to true when a single-global variable is set. This is sometimes called Staging Changes Before Going Live.
This allows us to set the global variable by various methods, and it also allows us to launch the changes to the public across various page templates by setting a single variable value to a truthy value.