Global element vs Local element in xsd

Global element declarations, global type definitions: These are element declarations/type definitions that are immediate children of Local element declarations, local type definitions: These are element declarations/type definitions that are nested within other elements/types.
So what if an element or type is global or local. What practical impact does it have? Answer: only global elements/types can be referenced (i.e., reused). Thus, if an element/type is local then it is effectively invisible to the rest of the schema (and to other schemas).