The client can use ZIP compression when sending data over the internet or across the LAN. Generally ZIP compression is not appropriate for LAN transfers due to the higher bandwidth usually available on a LAN connections. Both local and remote computers need to have ZIP compression selected for it to be used.
It is possible to control the use of ZIP compression separately for LAN connections. For WAN transfers it can't be disabled.
ZIP compression is turned on by default for WAN connections and disabled for LAN. To enable/disable the feature: