This policy setting allows the client application to open a document directly from the Office Document Cache if it is aware ...

This policy setting allows the client application to open a document directly from the Office Document Cache if it is aware that the server the document resides on is not reachable. It may be useful in situations where you would like to wait to contact the server every time, time out and then fallback to the cache. 

If you enable or do not configure this policy setting, documents will be opened directly from the Office Document Cache when the server the document resides on is not reachable. 

If you disable this policy setting, Office will always attempt to first reach the server the document resides on before opening it from the Office Document Cache.