Layer Variables applies properties to a Variable that are specific to the Layer your parametric is on. If a variable is designated as a Layer Variable it is instantly given the properties to be used in that single layer and overrides any Project Variable with the same name.
To access this functionality simply click the Layer Variables button to activate. All variables entered will be assigned these properties.
This type of variable can also be used in Expressions created for specific parts in a single layer.
This tool should be used for specific targeted formulas or when an override is necessary for that particular layer.