user reported no temperature difference between chassis having or not having the rear cable cover, however, to me the white (lunar) rear cable cover is desirable for esthetics. from the side the R13 chassis without rear cover is like an integral piece is missing, leaving a concave defect (waning moon).  the rear cover renders a whole moon view (full moon).  the magnetic mounting mechanism is also super easy.  kudos to Dell design. [IMAGE] [IMAGE]  
for additional $50 you can get the rear cable cover when you order R13 but if you opted not, your product spec would say   but if you got your R13 and want the cover, here is DP/N     ($114.99 before taxes; currently out of stock)   320-BENR : Lunar Light Rear Cable Cover [IMAGE][IMAGE][IMAGE]   $114.99+taxes, yes it is in stock (Dell chat)
Aurora R13, magnetic rear cable cover