Complex sentence: If a device already has power available but no data link, then a wireless data connection such as IEEE 802.11 may be more economical than running a data/POE cable for the device.
Split into simpler sentences: If a device already has power available but no data link, then PoE may not be attractive. A wireless data connection such as IEEE 802.11 may be more economical than running a data cable for the device.